Calcium receptor-active molecules

ABSTRACT

The present invention relates to the different roles inorganic ion receptors have in cellular and body processes. The present invention features: (1) molecules which can modulate one or more inorganic ion receptor activities, preferably the molecule can mimic or block an effect of an extracellular ion on a cell having an inorganic ion receptor, more preferably the extracellular ion is Ca 2+   and the effect is on a cell having a calcium receptor; (2) inorganic ion receptor proteins and fragments thereof, preferably calcium receptor proteins and fragments thereof; (3) nucleic acids encoding inorganic ion receptor proteins and fragments thereof, preferably calcium receptor proteins and fragments thereof; (4) antibodies and fragments thereof, targeted to inorganic ion receptor proteins, preferably calcium receptor protein; and (5) uses of such molecules, proteins, nucleic acids and antibodies.

RELATED APPLICATIONS

This is a continuation-in-part of Nemeth et al., entitled "CalciumReceptor Active Molecules" U.S. Ser. No. 08/353,784, filed Dec. 8, 1994,which is a continuation-in-part of Nemeth et al., entitled "CalciumReceptor Active Molecules" PCT/US94/12117, filed Oct. 21, 1994, and acontinuation-in-part of Nemeth et al., U.S. Ser. No. 08/292,827, filedAug. 19, 1994, now abandoned, entitled "Calcium Receptor ActiveMolecules" and a continuation-in-part of U.S. Ser. No. 08/141,248, filedOct. 22, 1993, now abandoned, entitled "Calcium Receptor ActiveMolecules" and a continuation-in-part of Nemeth et al., U.S. Ser. No.08/009,389, filed Feb. 23, 1993, now abandoned, entitled "CalciumReceptor Active Molecules", U.S. Ser. No. 08/292,827 is a continuationin part of U.S. Ser. No. 08/141,248, which is a continuation in part ofU.S. Ser. No. 08/009,389, a continuation-in-part of U.S. Ser. No.08/017,127, filed Feb. 12, 1993, now abandoned which is acontinuation-in-part of Nemeth et al., U.S. Ser. No. 07/934,161, nowabandoned, filed Aug. 21, 1992, which is a continuation-in-part ofNemeth et al., U.S. Ser. No. 07/834,044, filed Feb. 11, 1992, abandoned,which is a continuation-in-part of Nemeth et al., U.S. Ser. No.07/749,451, filed Aug. 23, 1991, abandoned, the whole of each of theseapplications including the drawings are hereby incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates to the design, development, composition and useof molecules able to modulate the activity of an inorganic ion receptor,preferably a calcium receptor. It also relates to a superfamily ofreceptors for inorganic ion (inorganic ion receptors) such as calciumreceptors. The invention also relates to nucleic acids encoding suchreceptors, cells, tissues and animals containing such nucleic acids,antibodies to such receptors, assays utilizing such receptors, andmethods relating to all of the foregoing.

BACKGROUND OF THE INVENTION

The following description provides a summary of information relevant tothe present invention. It is not an admission that any of theinformation provided herein is prior art to the presently claimedinvention, nor that any of the publications specifically or implicitlyreferenced are prior art to that invention.

Certain cells in the body respond not only to chemical signals, but alsoto ions such as extracellular calcium ions (C²⁺). Changes in theconcentration of extracellular Ca²⁺ (referred to herein as " C²⁺ !")alter the functional responses of these cells. One such specialized cellis the parathyroid cell which secretes parathyroid hormone (PTH). PTH isthe principal endocrine factor regulating. Ca²⁺ homeostasis in the bloodand extracellular fluids.

PTH, by acting on bone and kidney cells, increases the level of Ca²⁺ inthe blood. This increase in Ca²⁺ ! then acts as a negative feedbacksignal, depressing PTH secretion. The reciprocal relationship betweenCa²⁺ ! and PTH secretion forms the essential mechanism maintainingbodily Ca²⁺ homeostasis.

Extracellular Ca²⁺ acts directly on parathyroid cells to regulate PTHsecretion. The existence of a parathyroid cell surface protein whichdetects changes in Ca²⁺ ! has been suggested. This protein acts as areceptor for extracellular Ca²⁺ ("the calcium receptor"), and issuggested to detect changes in Ca²⁺ ! and to initiate a functionalcellular response, PTH secretion. For example, the role of calciumreceptors and extracellular Ca²⁺ in the regulation of intracellular Ca²⁺and cell function is reviewed in Nemeth et al., Cell Calcium 11: 319,1990; the role of calcium receptors in parafollicular and parathyroidcells is discussed in Nemeth, Cell Calcium 11: 323, 1990; and the roleof calcium receptors on bone osteoclasts is discussed by Zaidi,Bioscience Reports 10: 493, 1990.

Other cells in the body, specifically the osteoclast in bone, thejuxtaglomerular, proximal tubule cells in the kidney, the keratinocytein the epidermis, the parafollicular cell in the thyroid, intestinalcells, and the trophoblast in the placenta, have the capacity to sensechanges in Ca²⁺ !. It has been suggested that cell surface calciumreceptors may also be present on these cells, imparting to them theability to detect and to initiate or enable a response to changes inCa²⁺ !.

In parathyroid cells, osteoclasts, parafollicular cells (C-cells),keratinocytes, juxtaglomerular cells, trophoblasts, pancreatic betacells and fat/adipose cells, an increase in Ca²⁺ ! evokes an increase inintracellular free Ca²⁺ concentration (" Ca²⁺ !_(i) "). Such an increasemay be caused by influx of extracellular Ca²⁺ or by mobilization of Ca²⁺from intracellular organelles. Changes in Ca²⁺ !_(i) are readilymonitored and quantitated using fluorimetric indicators such as fura-2or indo-1 (Molecular Probes, Eugene, Oreg.). Measurement of Ca²⁺ !_(i)provides an assay to assess the ability of molecules to act as agonistsor antagonists at the calcium receptor.

In parathyroid cells, increases in the concentration of extracellularCa²⁺ evoke rapid and transient increases in Ca²⁺ !_(i) which arefollowed by lower, yet sustained, increases in Ca²⁺ !_(i). The transientincreases in Ca²⁺ !_(i) arise from the mobilization of intracellularCa²⁺, whereas the lower, sustained increases result from the influx ofextracellular Ca²⁺. The mobilization of intracellular Ca²⁺ isaccompanied by increased formation of inositol-1,4,5-triphosphate (IP₃)and diacylglycerol, two biochemical indicators which are associated withreceptor-dependent mobilization of intracellular Ca²⁺ in various othercells.

In addition to Ca²⁺, various other di- and trivalent cations, such asMg²⁺, Sr²⁺, Ba²⁺, La³⁺ and Gd³⁺ also cause the mobilization ofintracellular Ca²⁺ in parathyroid cells. Mg²⁺ and La³⁺ also increase theformation of IP₃. All of these inorganic cations depress the secretionof PTH. The postulated calcium receptor on the parathyroid cell istherefore promiscuous because it detects a variety of extracellular di-and trivalent cations.

The ability of various compounds to mimic extracellular. Ca²⁺ in vitrois discussed by Nemeth et al., (spermine and spermidine) in"Calcium-Binding Proteins in Health and Disease," 1987, Academic Press,pp. 33-35; Brown et al., (e.g., neomycin) Endocrinology 128: 3047, 1991;Chen et al., (diltiazem and its analog, TA-3090) J. Bone and MineralRes. 5: 581, 1990; and Zaidi et al., (verapamil) Biochem. Biophys. Res.Commun. 167: 807, 1990.

Brown et al., J. Bone Mineral Res. 6: 11, 1991 discuss theoriesregarding the effects of Ca²⁺ ions on parathyroid cells, and proposethat the results may be explained by both a receptor-like mechanism anda receptor-independent mechanism as follows:

Polyvalent cations e.g., divalent and trivalent cations! exert a varietyof effects on parathyroid function, such as inhibition of parathyroidhormone (PTH) secretion and cAMP accumulation, stimulation of theaccumulation of inositol phosphates, and elevation of the cytosoliccalcium concentration. These actions are thought to be mediated througha "receptor-like" mechanism. The inhibition of agonist-stimulated cAMPaccumulation by divalent and trivalent cations, for example, is blockedfollowing preincubation with pertussis toxin. Thus, the putativepolyvalent cation receptor may be coupled to inhibition of adenylatecyclase by the inhibitory guanine nucleotide regulatory (G) protein,G_(i).

We recently showed that the polycationic antibiotic, neomycin, mimicsthe actions of di- and trivalent cations in several aspects ofparathyroid function. To determine whether these actions were specificto this agent or represented a more generalized action of polycations,we tested the effects of the highly basic peptides, polyarginine andpolylysine, as well as protamine on the same parameters in dispersedbovine parathyroid cells. The results demonstrate that the parathyroidcell responds to a variety of polycations as well as to polyvalentcations, potentially via similar Biochemical pathways. These results arediscussed in terms of the recently postulated, "receptor-independent"modulation of G proteins by polycations in other systems.

The Ca²⁺ receptor has been presumed to be analogous to other Gprotein-coupled receptors e.g., a glycoprotein!, but recent studies withother cell types have raised the possibility that polycations canmodulate cell function by alternative or additional mechanisms. In mastcells, for example, a variety of amphipathic cations, includingmastoparan, a peptide from wasp venom, 48/80, a synthetic polycation,and polylysine, enhance secretion by a pertussis toxin-sensitivemechanism, suggesting the involvement of a G protein. No classic cellsurface receptor has been identified that could mediate the actions ofthese diverse agents. Furthermore, these same compounds have been shownto activate directly purified .G proteins in solution or in artificialphospholipid vesicles. On the basis of these observations, it has beenproposed that amphipathic cations activate G proteins and, in turn, mastcell secretion by a "receptor-independent" mechanism.

Polycations have also been shown to interact strongly with acidicphospholipids. Polylysines of varying chain lengths (20-1000 aminoacids) bind to artificial phospholipid vesicles with dissociationconstants in the range of 0.5 nM to 1.5 μM. The binding affinity isdirectly related to the length of the polylysine chain, with polymers of1000 amino acids having a K_(d) of 0.5 nM, shorter polymers havinghigher Kd values, and lysine not interacting to a significant extent.This relationship between potency and chain length is similar to thatobserved for the effects of polylysine 10,200, polylysine 3800, andlysine on parathyroid function.

It is possible that the binding of polycations to biomembranes producessome of their biologic actions. The permeabilization of the plasmamembrane induced in some cell types by a variety of pore-forming agents,including polycations, has been postulated to be mediated by theirinteraction with a phosphatidylserine-like structure. In addition, the"receptor-independent" activation of purified G proteins by amphipathiccations is potentiated when these proteins are incorporated intophospholipid vesicles.

Calcium ions, in the millimolar concentration range, also produce markedchanges in membrane structure. In some cases, calcium can eitherantagonize or potentiate the interaction of polycations with membranelipids. These considerations raise the possibility that the actions ofboth polyvalent cations and polycations on parathyroid cells couldinvolve a receptor-independent mechanism not requiring the presence of aclassic, cell surface, G protein-coupled receptor. Further studies,however, are required to elucidate the molecular basis for Ca²⁺ sensingby this and other cell types. Citations omitted.!

Shoback and Chen, J. Bone Mineral Res. 6 (Supplement 1) 1991, S135) andRacke et al., J. Bone Mineral Res. 6 (Supplement 1) 1991, S118) describeexperiments which are said to indicate that a calcium receptor or Ca²⁺sensor is present in parathyroid cells. Messenger RNA isolated from suchcells can be expressed in oocytes and caused to provide those oocyteswith a phenotype which might be explained by the presence of a calciumreceptor protein.

SUMMARY OF THE INVENTION

The present invention relates to the different roles inorganic ionreceptors have in cellular and body processes. The present inventionfeatures: (1) molecules which can modulate one or more inorganic ionreceptor activities, preferably the molecule can mimic or block aneffect of an extracellular ion on a cell having an inorganic ionreceptor, more preferably the extracellular ion is Ca²⁺ and the effectis on a cell having a calcium receptor; (2) inorganic ion receptorproteins and fragments thereof, preferably calcium receptor proteins andfragments thereof; (3) nucleic acids encoding inorganic ion receptorproteins and fragments thereof, preferably calcium receptor proteins andfragments thereof; (4) antibodies and fragments thereof, targeted toinorganic ion receptor proteins, preferably calcium receptor protein;and (5) uses of such molecules, proteins, nucleic acids and antibodies.

The preferred use of the present invention is to treat diseases ordisorders in a patient by modulating one or more inorganic ion receptoractivities. Diseases or disorders which can be treated by modulatinginorganic ion receptor activity include one or more of the followingtypes: (1) those characterized by abnormal inorganic ion homeostasis;(2) those characterized by an abnormal amount of an extracellular orintracellular messenger whose production can be affected by inorganicion receptor activity; (3) those characterized by an abnormal effect(e.g., a different effect in kind or magnitude) of an intracellular orextracellular messenger which can itself be ameliorated by inorganic ionreceptor activity; and (4) other diseases or disorders in whichmodulation of inorganic ion receptor activity will exert a beneficialeffect, for example, in diseases or disorders where the production of anintracellular or extracellular messenger stimulated by receptor activitycompensates for an abnormal amount of a different messenger. Examples ofextracellular messengers whose secretion and/or effect can be affectedby modulating inorganic ion receptor activity include inorganic ions,hormones, neurotransmitters, growth factors, and chemokines. Examples ofintracellular messengers include cAMP, cGMP, IP₃, and diacylglycerol.

Preferably, the compound modulates calcium receptor activity and is usedin the treatment of diseases or disorders which can be affected bymodulating one or more activities of a calcium receptor. ExtracellularCa²⁺ is under tight homeostatic control and controls various processessuch as blood clotting, nerve and muscle excitability, and proper boneformation. Calcium receptor proteins enable certain specialized cells torespond to changes in extracellular Ca²⁺ concentration. For example,extracellular Ca²⁺ inhibits the secretion of parathyroid hormone fromparathyroid cells, inhibits bone resorption by osteoclasts, andstimulates secretion of calcitonin from C-cells.

Preferably, the disease or disorder is characterized by abnormal boneand mineral .homeostasis., more preferably calcium homeostasis. Abnormalcalcium homeostasis is characterized by one or more of the followingactivities: (1) an abnormal increase or decrease in serum calcium; (2)an abnormal increase or decrease in urinary excretion of calcium; (3) anabnormal increase or decrease in bone calcium levels, for example, asassessed by bone-mineral density measurements; (4) an abnormalabsorption of dietary calcium; (5) an abnormal increase or decrease inthe production and/or release of messengers which affect serum calciumlevels such as parathyroid hormone and calcitonin; and (6) an abnormalchange in the response elicited by messengers which affect serum calciumlevels. The abnormal increase or decrease in these different aspects ofcalcium homeostasis is relative to that occurring in the generalpopulation and is generally associated with a disease or disorder.Diseases and disorders characterized by abnormal calcium homeostasis canbe due to different cellular defects such as a defective calciumreceptor activity or a defective intracellular protein acted on by acalcium receptor. For example, in parathyroid cells, the calciumreceptor is coupled to the G_(i) protein which in turn inhibits cyclicAMP production. Defects in G_(i) protein can affect its ability toinhibit cyclic AMP production.

The inorganic ion receptor-modulating agents (e.g., molecules andcompositions) can be used to treat patients. A "patient" refers to amammal in which modulation of an inorganic ion receptor will have abeneficial effect. Patients in need of treatment involving modulation ofinorganic ion receptors can be identified using standard techniquesknown to those in the medical profession. Preferably, a patient is ahuman having a disease or disorder characterized by one more of thefollowing: (1) abnormal inorganic ion homeostasis, more preferablyabnormal calcium homeostasis; (2) an abnormal level of a messenger whoseproduction or secretion is affected by inorganic ion receptor activity,more preferably affected by calcium receptor activity; and (3) anabnormal level or activity of a messenger whose function is affected byinorganic ion receptor activity, more preferably affected by calciumreceptor activity.

Thus, a first aspect of the present invention features an inorganic ionreceptor-modulating agent comprising a molecule which either evokes oneor more inorganic ion receptor activities, or blocks one or moreinorganic ion receptor activities. The agent has an EC₅₀ of less than orequal to 5 μM at its respective receptor and is not protamine.Preferably, the inorganic ion receptor is a calcium receptor and themolecule has an EC₅₀ of less than or equal to 5 μM at a calcium receptorand is not protamine.

Inorganic ion receptor activities are those processes brought about as aresult of inorganic ion receptor activation. Such processes include theproduction of molecules which can act as intracellular or extracellularmessengers.

Inorganic ion receptor-modulating agents include ionomimetics,ionolytics, calcimimetics, and calcilytics. Ionomimetics are moleculeswhich bind to an inorganic ion receptor and mimics (i.e., evokes orpotentiates) the effects of an inorganic ion at an inorganic ionreceptor. Preferably, the molecule affects one or more calcium receptoractivities. Calcimimetics are ionomimetics which affect one or morecalcium receptor activities and bind to a calcium receptor.

Ionolytics are molecules which bind to a inorganic ion receptor andblock (i.e., inhibits or diminishes) one or more activities caused by aninorganic ion on an inorganic ion receptor. Preferably, the moleculeaffects one or more calcium receptor activities. Calcilytics areionolytics which inhibit one or more calcium receptor activities evokedby extracellular calcium and bind to a calcium receptor.

Ionomimetics and ionolytics may bind at the same receptor site as thenative inorganic ion ligand binds or can bind at a different site (e.g.,allosteric site). For example, NPS R-467 binding to a calcium receptorresults in calcium receptor activity and, thus, NPS R-467 is classifiedas a calcimimetic. However, NPS R-467 binds to the calcium receptor at adifferent site (i.e., an allosteric site) than extracellular calcium.

The EC₅₀ is the concentration of agent which causes a half maximalmimicking effect. For example, the EC₅₀ for calcium receptor activitiescan be determined by assaying one or more of the activities ofextracellular calcium at a calcium receptor- Examples of suitable assaysfor measuring EC₅₀ are described herein and include oocyte expressionassays and measuring increases in intracellular calcium due to calciumreceptor activity. Preferably, such assays measure the release orinhibition of a particular hormone associated with activity of a calciumreceptor.

An inorganic ion receptor-modulating agent preferably selectivelytargets inorganic ion receptor activity in a particular cell. Forexample, selective targeting of a calcium receptor activity is achievedby an agent exerting a greater effect on a calcium receptor activity inone cell type than at another cell type for a given concentration ofagent. Preferably, the differential effect is 10-fold or greater asmeasured in vivo or in vitro. More preferably, the differential effectis measured in vivo and the agent concentration is measured as theplasma concentration or extracellular fluid concentration and themeasured effect is the production of extracellular messengers such asplasma calcitonin, parathyroid hormone, or plasma calcium. For example,in a preferred embodiment, the agent selectively targets PTH secretionover calcitonin secretion.

In one embodiment concerning the structure of the inorganic ionreceptor-modulating agent, the molecule is positively charged atphysiological pH, and is selected from the group consisting of branchedor cyclic polyamines, positively charged polyamino acids, andarylalkylamines. Preferably, the branched polyamine has the formula H₂N--(CH₂)_(j) --(NR_(i) --(CH₂)_(j))_(k) --NH₂ where k is an integer from1 to 10, each j is the same or different and is an integer from 2 to 20,and each R_(i) is the same or different and is selected from the groupconsisting of hydrogen and --(CH₂)_(j) --NH₂, where j is as definedabove, and at least one R_(i) is not hydrogen. Preferably, the inorganicion receptor-modulating agent can modulate one or more calcium receptoractivities.

In a preferred embodiment concerning the structure of inorganic ionreceptor-modulating agents the arylalkylamine molecule has the formula:##STR1##

where each X independently is selected from the group consisting of H,CH₃, CH₃ O, CH₃ CH₂ O, methylene dioxy, Br, Cl, F, I, CF₃, CHF₂, CH₂ F,CF₃ O, CF₃ CH₂ O, CH₃ S, OH, CH₂ OH, CONH₂, CN, NO₂, CH₃ CH₂, propyl,isopropyl, butyl, isobutyl, t-butyl, and acetoxy;

Ar is a hydrophobic entity;

each R independently is selected from the group consisting of hydrogen,methyl, ethyl, propyl, isopropyl, allyl, butyl, isobutyl, t-butyl,cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, indenyl, indanyl,dihydroindolyl, thiodihydroindolyl, and 2-, 3-, or 4- piperid(in)yl;

Y is selected from the group consisting of CH, nitrogen and anunsaturated carbon; and

Z is selected from the group consisting of oxygen, nitrogen, sulfur,##STR2##

where each n is independently between 1 and 4 inclusive; and

each m is independently between 0 and 5 inclusive.

A hydrophobic entity refers to a non-polar group or moiety such as anaromatic or a cycloaliphatic ring or ring system. Preferably, thehydrophobic entity is selected from the group consisting of phenyl,cyclohexyl, 2-, 3-, or 4-pyridyl, 1- or 2-naphthyl, α- orβ-tetrahydronaphthyl, 1- or 2-quinolinyl, 2- or 3-indolyl, benzyl, andphenoxy.

More preferably, the inorganic ion receptor-modulating agent is asubstituted R-phenylpropyl-α-phenethylamine, substitutedR-benzyl-α-1-napthylethylamine analogues, and derivatives having theformula: ##STR3##

where alk is straight- or branched-chain alkylene of from 0 to 6 carbonatoms;

R₁ is lower alkyl of from 1 to 3 carbon atoms or lower haloalkyl of from1 to 3 carbon atoms substituted with from 1 to 7 halogen atoms;

R₂ and R₃ are independently selected carbocyclic aryl or cycloalkylgroups, either monocyclic or bicyclic, having 5- to 7-membered ringsoptionally substituted with 1 to 5 substituents independently selectedfrom lower alkyl of 1 to 3 carbon atoms, lower haloalkyl of 1 to 3carbon atoms substituted with 1 to 7 halogen atoms, lower alkoxy of 1 to3 carbon atoms, halogen, nitro, amino, alkylamino, amido, loweralkylamido of 1 to 3 carbon atoms, cyano, hydroxy, acyl of 2 to 4 carbonatoms, lower hydroxyalkyl of 1 to 3 carbon atoms or lower thioalkyl of 1to 3 carbon atoms. Suitable carbocyclic aryl groups are groups havingone or two rings, at least one of which has aromatic character andinclude carbocyclic aryl groups such as phenyl and bicyclic carbocyclicaryl groups such as naphthyl.

Preferred compounds include those where alk is n-propylene, methylene,or R-methyl methinyl. Also preferred are compounds where R₁ is R-methyl.Also preferred are those compounds where R₂ and R₃ are optionallysubstituted phenyl or naphthyl.

More preferred compounds are those where R₂ is monosubstituted phenyl,more preferably meta-substituted; or 1-naphthyl. More preferred R₃groups are unsubstituted or monosubstituted phenyl, especially meta- orortho-substituted, or 2-naphthyl. Preferred substituents for R₂ arehalogen, haloalkyl, preferably trihalomethyl, alkoxy, preferablymethoxy, and thioalkyl, preferably thiomethyl. Preferred substituentsfor R₃ are meta- or ortho-halogen, preferably chlorine, fluorine, or CF₃and para- or ortho-alkoxy, preferably methoxy, and meta-lower alkyl,preferably methyl.

As is apparent from the above formula, preparation of the molecules mayresult in racemic mixtures containing individual stereoisomers. Morepreferred compounds are R-phenylpropyl-α-phenethylamine andR-benzyl-α-1-napthylethlamine derivatives which are believed to exhibitenhanced activity in lowering serum ionized calcium.

More preferably, the molecule is a substitutedR-phenylpropyl-α-phenethylamine derivative, or a substitutedR-benzyl-α-phenethylamine derivative, having the structure: ##STR4##

where each X is preferably independently selected from the groupconsisting of Cl, F, I, CF₃, CH₃, isopropyl, CH₃ O, CH₃ S, CF₃ O, CF₃CH₂ O, an aliphatic ring and an attached or fused, preferably fusedaromatic ring. Preferably, the aromatic and aliphatic rings have 5 to 7members. More preferably, the aromatic and aliphatic rings contain onlycarbon atoms (i.e., the ring is not a heterocyclic ring); and

R is preferably H, CH₃, ethyl, or isopropyl.

In more preferred embodiments the molecule inhibits. parathyroid hormonesecretion from a parathyroid cell; inhibits bone resorption in vivo byan osteoclast; inhibits bone resorption in vitro by an osteoclast;stimulates calcitonin secretion in vitro or in vivo from a c-cell; orthe molecule evokes the mobilization of intracellular Ca²⁺ to cause anincrease in Ca²⁺ !_(i).

Preferably, the molecule is either a calcimimetic or calcilytic havingan EC₅₀ or IC₅₀ at a calcium receptor of less than or equal to 5 μM, andeven more preferably less than or equal to 1 μM, 100 nmolar, 10 nmolar,or 1 nmolar. Such lower EC₅₀ 's or IC₅₀ 's are advantageous since theyallow lower concentrations of molecules to be used in vivo or in vitrofor therapy or diagnosis. The discovery of molecules with such low EC₅₀'s and IC₅₀ 's enables the design and synthesis of additional moleculeshaving similar or improved potency, effectiveness, and/or selectivity.

In another preferred embodiment, the molecule has an EC₅₀ or IC₅₀ lessthan or equal to 5 μM at one or more, but not all cells chosen from thegroup consisting: of parathyroid cell, bone osteoclast, juxtaglomerularkidney cell, proximal tubule kidney cell, distal tubule kidney cell,central nervous system cell, peripheral nervous system cell, cell of thethick ascending limb of Henle's loop and/or collecting duct,keratinocyte in the epidermis, parafollicular cell in the thyroid(C-cell), intestinal cell, trophoblast in the placenta, platelet,vascular smooth muscle cell, cardiac atrial cell, gastrin-secretingcell, glucagon-secreting cell, kidney mesangial cell, mammary cell, betacell, fat/adipose cell, immune cell, GI tract cell, skin cell, adrenalcell, pituitary cell, hypothalamic cell and cell of the subfornicalorgan.

More preferably, the cells are chosen from the group consisting ofparathyroid cell, central nervous system cell, peripheral nervous systemcell, cell of the thick ascending limb of Henle's loop and/or collectingduct in the kidney, parafollicular cell in the thyroid (C-cell),intestinal cell, GI tract cell, pituitary cell, hypothalamic cell andcell of the subfornical organ. This presence of a calcium receptor inthis group of cells hah been confirmed by physical data such as in situhybridization and antibody staining.

Another aspect of the present invention features a calciumreceptor-modulating agent comprising a molecule selected from the groupconsisting of: NPS R-467, NPS R-568, compound 1D, compound 3U, compound3V, compound 4A, compound 4B, compound 4C, compound 4D, compound 4G,compound 4H, compound 4J, compound 4M, compound 4N, compound 4P,compound 4R/6V, compound 4S, compound 4T/4U, compound 4V, compound 4W,compound 4Y, compound 4Z/5A, compound 5B/5C, compound 5W/5Y, compound6E, compound 6F, compound 6R, compound 6T, compound 6X, compound 7W,compound 7X, compound 8D, compound 8J, compound 8K, compound 8R,compound 8S, compound 8T, compound 8U, compound 8X, compound 8Z,compound 9C, compound 9D, compound 9R, compound 9S, compound 10F,compound 11D, compound 11X, compound 11Y, compound 12L, compound 12U,compound 12V, compound 12W, compound 12Y, compound 13Q, compound 13R,compound 13S, compound 13U, compound 13X, compound 14L, compound 14Q,compound 14U, compound 14V, compound 14Y, compound 15G, compound 16Q,compound 16R, compound 16T, compound 16V, compound 16W, compound 16X,compound 17M, compound 17O, compound 17P, compound 17R, compound 17W;compound 17X, compound 20F, compound 20I, compound 20J, compound 20R,compound 20S, compound 21D, compound 21F, compound 21G, compound 21O,compound 21P, compound 21Q, and compound 21R (see FIG. 36).

Another aspect of the present invention features a pharmaceuticalcomposition made up of an inorganic ion receptor-modulating agent and aphysiologically acceptable carrier. Such agents can be used to treatpatients by modulating inorganic ion receptor activity.

Prior to this invention, applicant was unaware of any agent acting onthe calcium receptor useful in the treatment of diseases caused byirregularity in operation or regulation of a calcium receptor or indiseases in an animal having normal calcium receptors, but which can betreated by modulating calcium activity.

A pharmacological agent or composition refers to an agent or compositionin a form suitable for administration into a mammal, preferably a human.Considerations concerning forms suitable for administration are known inthe art and include toxic effects, solubility, route of administration,and maintaining activity. For example, pharmacological agents orcompositions injected into the blood stream should be soluble.

Pharmaceutical compositions can also be formulated as pharmaceuticallyacceptable salts (e.g., acid addition salts) and complexes thereof. Thepreparation of such salts can facilitate the pharmacological use of anagent by altering its physical characteristics without preventing itfrom exerting a physiological effect.

Another aspect of the present invention features a method for modulatinginorganic ion receptor activity, preferably calcium receptor activity.The method involves the step of providing to a cell comprising aninorganic ion receptor an amount of an inorganic ion receptor-modulatingmolecule sufficient to either mimic one or more effects of an inorganicion at the inorganic ion receptor, or block one or more effects of theinorganic ion at the inorganic ion receptor. The method can carried outin vitro or in vivo.

Preferably, the molecule is either a calcimimetic or a calcilytic whichmodulates one or more calcium receptor activity. Examples of calciumreceptor-modulating molecules or agents are described herein. Additionalcalcium receptor-modulating agents can be obtained based on the presentdisclosure. More preferably, the method is carried out in vivo to treata patient.

Another aspect the present invention features a method for treating apatient by modulating inorganic ion receptor activity. The methodinvolves administering to the patient a therapeutically effective amountof an inorganic ion receptor-modulating agent.

In a preferred embodiment, the disease or disorder is treated bymodulating calcium receptor activity by administering to the patient atherapeutically effective amount of a calcium receptor-modulating agent.

Preferably the disease or disorder is characterized by one or more ofthe following: (1) abnormal inorganic ion homeostasis, more preferablyabnormal calcium homeostasis; (2) an abnormal level of a messenger whoseproduction or secretion is affected by inorganic ion receptor activity,more preferably affected by calcium receptor activity; and (3) anabnormal level or activity of a messenger whose function is affected byinorganic ion receptor activity, more preferably affected by calciumreceptor activity.

Diseases characterized by abnormal calcium homeostasis includehyperparathyroidism, osteoporosis and other bone and mineral-relateddisorders, and the like (as described, e.g., in standard medical textbooks, such as. "Harrison's Principles of Internal Medicine"). Suchdiseases are treated using calcium receptor-modulating agents whichmimic or block one or more of the effects of extracellular Ca²⁺ on acalcium receptor and, thereby, directly or indirectly affect the levelsof proteins or other molecules in the body of the patient.

By "therapeutically effective amount" is meant an amount of an agentwhich relieves to some extent one or more symptoms of the disease ordisorder in the patient; or returns to normal either partially orcompletely one or more physiological or biochemical parametersassociated with or causative of the disease.

In a preferred embodiment, the patient has a disease or disordercharacterized by an abnormal level of one or more calciumreceptor-regulated components and the molecule is active on a calciumreceptor of a cell selected from the group consisting of: parathyroidcell, bone osteoclast, juxtaglomerular kidney cell, proximal tubulekidney cell, distal tubule kidney cell, central nervous system cell,peripheral nervous system cell, cell of the thick ascending limb ofHenle's loop and/or collecting duct, keratinocyte in the epidermis,parafollicular cell in the thyroid (C-cell), intestinal cell,trophoblast in the placenta, platelet, vascular smooth muscle cell,cardiac atrial cell, gastrin-secreting cell, glucagon-secreting cell,kidney mesangial cell, mammary cell, beta cell, fat/adipose cell, immunecell, GI tract cell, skin cell, adrenal cell, pituitary cell,hypothalamic cell and cell of the subfornical organ.

More preferably, the cells are chosen from the group consisting of:parathyroid cell, central nervous system cell, peripheral nervous systemcell, cell of the thick ascending limb of Henle's loop and/or collectingduct-in the kidney, parafollicular cell in the thyroid (C-cell),intestinal cell, GI tract cell, pituitary cell, hypothalamic cell andcell of the subfornical organ.

In a preferred embodiment, the agent is a calcimimetic acting on aparathyroid cell calcium receptor and reduces the level of parathyroidhormone in the serum of the patient. More preferably, the level isreduced to a degree sufficient to cause a decrease in plasma Ca²⁺. Mostpreferably, the parathyroid hormone level is reduced to that present ina normal individual.

In another preferred embodiment, the agent is a calcilytic acting on aparathyroid cell calcium receptor and increases the level of parathyroidhormone in the serum of the patient. More preferably, the level isincreased to a degree sufficient to cause an increase in bone mineraldensity of a patient.

In another aspect, the invention features a method for diagnosing adisease or disorder in a patient characterized by an abnormal number ofinorganic ion receptors, or an altered inorganic ion receptors. Themethod involves identifying the number and/or location and/or functionalintegrity of one or more inorganic ion receptor. The number and/orlocation and/or functional integrity is compared with that observed inpatients characterized as normal or diseased as an indication of thepresence of the disease or disorder.

Diagnoses can be carried out using inorganic ion receptor-bindingagents. For example, calcium receptor-modulating agents binding tocalcium receptors, and antibodies which bind to calcium receptors, canbe used for diagnoses. Preferably, binding agents are labeled with adetectable moiety, such as a radioisotope or alkaline phosphatase.

An altered receptor has a different structure than the receptor has innormal individuals and is associated with a disease or disorderinvolving an inorganic ion receptor. Such alterations may affectreceptor function, and can be detected by assaying for a structuraldifference between the altered and normal receptor. Binding agents whichbind to an altered receptor, but not to a normal receptor, can be usedto determine the presence of an altered receptor. Additionally, abinding agent which can bind to a normal receptor, but not to aparticular altered receptor, can be used to determine the presence ofthe particular altered receptor.

Similarly, the number of receptors can be determined by using agentsbinding to the tested-for receptor. Such assays generally involve usinga labeled binding agent and can be carried out using standard formatssuch as competitive, non-competitive, homogenous, and heterogenousassays.

In other preferred embodiments, the method is an immunoassay in which anantibody to a calcium receptor is used to identify the number and/orlocation and/or functional integrity of the calcium receptors; the assayinvolves providing a labeled calcimimetic or calcilytic molecule; thepresence of a cancer, e.g., an ectopic tumor of the parathyroid, istested for by measuring calcium receptor number or alteration; andconditions characterized by an above-normal number of osteoclasts inbone or an increased level of activity of osteoclasts in bone is testedfor by measuring the number of calcium receptors.

In another aspect, the invention features a method for identifying amolecule useful as a therapeutic molecule to modulate inorganic ionreceptor activity or as a diagnostic agent to diagnose patientssuffering from a disease characterized by an abnormal inorganic ionactivity. Preferably, the method is used to identify calcimimetics orcalcilytics by screening potentially useful molecules for an ability tomimic or block an activity of extracellular Ca²⁺ on a cell having acalcium receptor and determining whether the molecule has an EC₅₀ orIC₅₀ of less than or equal to 5 μM. More preferably, the molecule istested for its ability to mimic or block an increase in Ca²⁺ !_(i)elicited by extracellular Ca²⁺.

Identification of inorganic ion receptor-modulating agents isfacilitated by using a high-throughput screening system. High-throughputscreening allows a large number of molecules to be tested. For example,a large number of molecules can be tested individually using rapidautomated techniques or in combination using a combinational library.Individual compounds able to modulate inorganic ion receptor activitypresent in a combinational library can be obtained by purifying andretesting fractions of the combinational library. Thus, thousands tomillions of molecules can be screened in a single day.

Active molecules can be used as models to design additional moleculeshaving equivalent or increased activity. Preferably, the identificationmethod uses a recombinant inorganic ion receptor, more preferably arecombinant calcium receptor. Recombinant receptors can be introducedinto different cells using a vector encoding the receptor.

Preferably, the activity of molecules in different cells is tested toidentify a calcimimetic or calcilytic molecule which mimics or blocksone or more activities of Ca²⁺ at a first type of calcium receptor, butnot at a second type of calcium receptor.

Another aspect of the present invention features a purified nucleic acidcontaining at least 12 contiguous nucleotides of a nucleic acid sequenceprovide in SEQ. ID. NO. 1, SEQ. ID. NO. 2, SEQ. ID. NO. 3 or SEQ. ID.NO. 4. By "purified" in reference to nucleic acid is meant the nucleicacid is present in a form (i.e., its association with other molecules)other than found in nature. For example, purified receptor nucleic acidis separated from one or more nucleic acids which are present on thesame chromosome. Preferably, the purified nucleic acid is separated fromat least 90% of the other nucleic acids present on the same chromosome.

Another example of purified nucleic acid is recombinant nucleic acid.Preferably, recombinant nucleic acid contains nucleic acid encoding aninorganic ion receptor or receptor fragment cloned in an expressionvector. An expression vector contains the necessary elements forexpressing a cloned nucleic acid sequence to produce a polypeptides. Anexpression vector contains a promoter region (which directs theinitiation of RNA transcription) as well as the DNA sequences which,when transcribed into RNA, will signal synthesis initiation.

Recombinant nucleic acid may contain nucleic acid encoding for aninorganic ion receptor, receptor fragment, or inorganic ion receptorderivative, under the control of its genomic regulatory elements, orunder the control of exogenous regulatory elements including anexogenous promoter. By "exogenous" is meant a promoter that is notnormally coupled in vivo transcriptionally to the coding sequence forthe inorganic ion receptor. Preferably, the nucleic acid is provided asa substantially purified preparation representing at least 75%, morepreferably 85%, most preferably 95% of the total nucleic acids presentin the preparation.

Nucleic acid sequences provided in SEQ. ID. NO. 1, SEQ. ID. NO. 2, SEQ.ID. NO. 3, and SEQ. ID. NO. 4 each encode for a calcium receptor.Nucleic acid sequences encoding both full length calcium receptors,calcium receptor fragments, derivatives of full length calciumreceptors, and derivatives of calcium receptor fragments are useful inthe present invention.

Uses of nucleic acids encoding cloned receptors or receptor fragmentsinclude one or more the following: (1) producing receptor proteins whichcan be used, for example, for structure determination, to assay amolecule's activity on a receptor, and to obtain antibodies binding tothe receptor; (2) being sequenced to determine a receptor's nucleotidesequence which can be used, for example, as a basis for comparison withother receptors to determine conserved regions, determine uniquenucleotide sequences for normal and altered receptors, and to determinenucleotide sequences to be used as target sites for antisense nucleicacids, ribozymes, hybridization detection probes, or PCR amplificationprimers; (3) as hybridization detection probes to detect the presence ofa native receptor and/or a related receptor in a sample; and (4) as PCRprimers to generate particular nucleic acid sequence regions, forexample to generate regions to be probed by hybridization detectionprobes.

Preferably, the nucleic acid contains at least 14, more preferably atleast 20, more preferably at least 27, and most preferably at least 45,contiguous nucleic acids of a sequence provided in SEQ. ID. NO. 1, SEQ.ID. NO. 2, SEQ. ID. NO. 3, or SEQ. ID. NO. 4. Advantages oflonger-length nucleic acid include producing longer-length proteinfragments having the sequence of a calcium receptor which can be used,for example, to produce antibodies; increased nucleic acid probespecificity under higher stringent hybridization assay conditions; andmore specificity for related inorganic ion receptor nucleic acid underlower stringency hybridization assay conditions.

Another aspect of the present invention features a purified nucleic acidencoding an inorganic ion receptor or fragment thereof. The nucleic acidencodes at least 6 contiguous amino acids provided in SEQ. ID. NO. 5,SEQ. ID. NO. 6, SEQ. ID. NO. 7 or SEQ. ID. NO. 8. Due to the degeneracyof the genetic code, different combinations of nucleotides can code forthe same polypeptide. Thus, numerous inorganic ion receptors andreceptor fragments having the same amino acid sequences can be encodedfor by different nucleic acid sequences. In preferred embodiments, thenucleic acid encodes at least 12, at least 18, or at least 54 contiguousamino acids of SEQ. ID. NO. 5, SEQ. ID. NO. 6, SEQ. ID. NO. 7 or SEQ.ID. NO. 8.

Another aspect of the present invention features a purified nucleic acidhaving a nucleic acid sequence region of at least 12 contiguousnucleotides substantially complementary to a sequence region in SEQ. ID.NO. 1, SEQ. ID. NO. 2, SEQ. ID. NO. 3 or SEQ. ID. NO. 4. By"substantially complementary" is meant that the purified nucleic acidcan hybridize to the complementary sequence region in nucleic acidencoded by SEQ. ID. NO. 1, SEQ. ID. NO. 2, SEQ. ID. NO. 3 or SEQ. ID.NO. 4 under stringent hybridizing conditions. Such nucleic acidsequences are particularly useful as hybridization detection probes todetect the presence of nucleic acid encoding a particular receptor.Under stringent hybridization conditions, only highly complementarynucleic acid sequences hybridize. Preferably, such conditions preventhybridization of nucleic acids having 4 mismatches out of 20 contiguousnucleotides, more preferably 2 mismatches out of 20 contiguousnucleotides, most preferably one mismatch out of 20 contiguousnucleotides. In preferred embodiments, the nucleic acid is substantiallycomplementary to at least 20, at least 27, or at least 45, contiguousnucleotides provided in SEQ. ID. NO. 1, SEQ. ID. NO. 2, SEQ. ID. NO. 3,or SEQ. ID. NO. 4.

Another aspect of the present invention features a purified polypeptidehaving at least 6 contiguous amino acids of an amino acid sequenceprovided in SEQ. ID. NO. 5, SEQ. ID. NO. 6, SEQ. ID. NO. 7 or SEQ. ID.NO. 8. By "purified" in reference to a polypeptide is meant that thepolypeptide is in a form (i.e., its association with other molecules)distinct from naturally occurring polypeptide. Preferably, thepolypeptide is provided as a substantially purified preparationrepresenting at least 75%, more preferably 85%, most preferably 95% ofthe total protein in the preparation. In preferred embodiments, thepurified polypeptide has at least 12, 18, or 54 contiguous amino acidsof SEQ. ID. NO. 5, SEQ. ID. NO. 6, SEQ. ID. NO. 7 or SEQ. ID. NO. 8.

Preferred receptor fragments include those having functional receptoractivity, a binding site, epitope for antibody recognition (typically atsix amino acids), and/or a site which binds a calcimimetic orcalcilytic. Other preferred receptor fragments include those having onlyan extracellular portion, a transmembrane portion, an intracellularportion, and/or a multiple transmembrane portion (e.g., seventransmembrane portion). Such receptor fragments have various uses suchas being used to obtain antibodies to a particular region and being usedto form chimeric receptors with fragments of other receptors create anew receptor having unique properties.

The invention also features derivatives of full-length inorganic ionreceptors and fragments thereof having the same, or substantially thesame, activity as the full-length parent inorganic ion receptor orfragment. Such derivatives include amino acid addition(s),substitution(s), and deletion(s) to the receptor which do not preventthe derivative receptor from carrying out one or more of the activitiesof the parent receptor.

Another aspect of the present invention features a recombinant cell ortissue. The recombinant cell or tissue is made up of a recombinednucleic acid sequence encoding at least 6 contiguous amino acidsprovided in. SEQ. ID. NO. 5, SEQ. ID. NO. 6, SEQ. ID. NO. 7 or SEQ. ID.NO. 8 and a cell able to express the nucleic acid. Recombinant cellshave various uses including acting as biological factories to producepolypeptides encoded for by the recombinant nucleic acid, and forproducing cells containing a functioning calcium receptor. Cellscontaining a functioning calcium receptor can be used, for example, toscreen for calcimimetics or calcilytics.

In preferred embodiments, the recombinant nucleic acid encodes afunctioning calcium receptor, more preferably a human calcium receptor;the cell or tissue is selected from the group consisting of: parathyroidcell, bone osteoclast, juxtaglomerular kidney cell, proximal tubulekidney cell, distal tubule kidney cell, central nervous system cell,peripheral nervous system cell, cell of the thick ascending limb ofHenle's loop and/or collecting duct, keratinocyte in the epidermis,parafollicular cell in the thyroid (C-cell), intestinal cell,trophoblast in the placenta, platelet, vascular smooth muscle cell,cardiac atrial cell, gastrin-secreting cell, glucagon-secreting cell,kidney mesangial cell, mammary cell, beta cell, fat/adipose cell, immunecell, GI tract cell, skin cell, adrenal cell, pituitary cell,hypothalamic cell and cell of the subfornical organ; and the recombinantnucleic acid encodes at least 12, 18 or 54 continuous amino acids ofSEQ. ID. NO. 5, SEQ. ID. NO. 6, SEQ. ID. NO. 7 or SEQ. ID. NO. 8.

Another aspect of the present invention features a calciumreceptor-binding agent able to bind a polypeptide having an amino acidsequence of SEQ. ID. NO. 5, SEQ. ID. NO. 6, SEQ. ID. NO. 7 or SEQ. ID.NO. 8. The binding agent is preferably a purified antibody whichrecognizes an epitope present on a polypeptide having an amino acidsequence of SEQ. ID. NO. 5, SEQ. ID. NO. 6, SEQ. ID. NO. 7 or SEQ. ID.NO. 8. Other binding agents include molecules which bind to thereceptor, for example, calcimimetics and calcilytics binding to thecalcium receptor.

By "purified" in reference to an antibody is meant that the antibody isin a form (i.e., its association with other molecules) distinct fromnaturally occurring antibody, such as in a purified form. Preferably,the antibody is provided as a purified preparation representing at least1%, more preferably at least 50%, more preferably at least 85%, mostpreferably at least 95% of the total protein in the preparation.

Antibodies able to bind inorganic ion receptors have various uses suchas being used as therapeutic agents to modulate calcium receptoractivity; as diagnostic tools for determining calcium receptor numberand/or location and/or functional integrity to diagnose a Ca²⁺ -relateddisease; and as research tools for studying receptor synthesis,structure, and function. For example, antibodies targeted to the calciumreceptor are useful to elucidate which portion of the receptor aparticular molecule such as the natural ligand, a calcimimetic, orcalcilytic, binds.

In preferred embodiments, the binding agent binds to an extracellularregion of a calcium receptor and the binding agent binds to a calciumreceptor expressed in tissue or cells selected from the group consistingof: parathyroid cell, bone osteoclast, juxtaglomerular kidney cell,proximal tubule -kidney cell, distal tubule kidney cell, central nervoussystem cell, peripheral nervous system cell, cell of the thick ascendinglimb of Henle's loop and/or collecting duct, keratinocyte in theepidermis, parafollicular cell in the thyroid (C-cell), intestinal cell,trophoblast in the placenta, platelet, vascular smooth muscle cell,cardiac atrial cell, gastrin-secreting cell, glucagon-secreting cell,kidney mesangial cell, mammary cell, beta cell, fat/adipose cell, immunecell, GI tract cell, skin cell, adrenal cell, pituitary cell,hypothalamic cell and cell of the subfornical organ. More preferably,the cells are chosen from the group consisting of parathyroid cell,central nervous system cell, peripheral nervous system cell, cell of thethick ascending limb of Henle's loop and/or collecting duct in thekidney, parafollicular cell in the thyroid (C-cell), intestinal cell, GItract cell, pituitary cell, hypothalamic cell and cell of thesubfornical organ.

In other preferred embodiments, the binding agent is coupled to a toxin.Binding agents coupled to a toxin can be used to deliver the toxin to acell containing a particular receptor. For example, an antibody coupledto a toxin directed to a cancer cell characterized by an abnormalreceptor can selectively kill the cancer cell.

In other aspects, the invention provides transgenic, nonhuman mammalscontaining a transgene encoding an inorganic ion receptor or a geneaffecting the expression of an inorganic ion receptor and methods ofcreating a transgenic nonhuman mammal containing a transgene encoding aninorganic ion receptor. Preferably, these aspects use a calciumreceptor.

Transgenic nonhuman mammals are particularly useful as an in vivo testsystem for studying the effects of introducing an inorganic ionreceptor, preferably a calcium receptor; regulating the expression of aninorganic ion receptor, preferably a calcium receptor (i.e., through theintroduction of additional genes, antisense nucleic acids, orribozymes); and studying the effect of molecules which mimic or blockthe effect of inorganic ions on an inorganic ion receptor, preferablymimic or block the effect of calcium on a calcium receptor. In preferredembodiments, the transgene encodes a calcium receptor; alters theexpression of a calcium receptor; inactivates the expression of theinorganic ion receptor, preferably a calcium receptor; and up-regulatesor down-regulates the expression of the inorganic ion receptor,preferably a calcium receptor.

Another aspect of the present invention features a method for treating apatient by administering a therapeutically effective amount of nucleicacid encoding a functioning inorganic ion receptor. Preferably, nucleicacid encoding a functioning calcium receptor is administered to apatient having a disease or disorder characterized by one or more of thefollowing: (1) abnormal calcium homeostasis; (2) an abnormal level of amessenger whose production or secretion is affected by calcium receptoractivity; and (3) an abnormal level or activity of a messenger whosefunction is affected by calcium receptor activity. The nucleic acid canbe administered using standard techniques such through the use ofretroviral vectors and liposomes.

Another aspect of the present invention features a method for treating apatient by administering a therapeutically effective amount of a nucleicacid which inhibits expression of an inorganic ion receptor. Preferably,the administered nucleic acid inhibits expression of a calcium receptorand the disease or disorder is characterized by one or more of thefollowing: (1) abnormal calcium homeostasis; (2) an abnormal level of amessenger whose production or secretion is affected by calcium receptoractivity; and (3) an abnormal level or activity of a messenger whosefunction is affected by calcium receptor activity.

Nucleic acids able to inhibit expression of an inorganic ion receptorinclude anti-sense oligonucleotides, ribozymes and nucleic acid able tocombine through homologous recombination with an endogenous geneencoding the receptor. Target sites of inhibitory nucleic acid includepromoters, other regulatory agents acting on promoters, mRNA,pre-processed mRNA, and genomic DNA. Administration can be carried outby providing a transgene encoding the agent or by any other suitablemethod depending upon the use to which the particular method isdirected.

Another aspect of the present invention features a method foridentifying an inorganic ion receptor-modulating agent. The methodinvolves contacting a cell containing a recombinant nucleic acidencoding an inorganic ion receptor with the agent and detecting a changein inorganic ion receptor activity. Preferably, the method is used toidentify a calcium receptor-modulating agent.

Thus, the present invention features agents and methods useful in thediagnosis and treatment of a variety diseases and disorders by targetinginorganic ion receptor activity. For example, molecules mimickingexternal calcium may be used to selectively depress secretion ofparathyroid hormone from parathyroid cells, or depress bone resorptionby osteoclasts, or stimulate secretion of calcitonin from C-cells. Suchmolecules can be used to treat diseases characterized by abnormalcalcium homeostasis such as hyperparathyroidism and osteoporosis.

Other features and advantages of the invention will be apparent from thefollowing description of the preferred embodiments thereof and from theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a-1f depict representative molecules useful in the invention.

FIG. 2 is a graphical representation showing increases in Ca²⁺ !_(i)induced by extracellular Ca²⁺ in quin-2- or fura-2- loaded bovineparathyroid cells. The initial Ca²⁺ ! was 0.5 mM (using CaCl₂) and, ateach of the arrows, was increased in 0.5 mM increments.

FIGS. 3a-3c are graphical representations showing mobilization of Ca²⁺!_(i) in bovine parathyroid cells. The initial Ca²⁺ ! was 0.5 mM and wasdecreased to <1 μM by the addition of EGTA as indicated. (a)Extracellular Mg²⁺ (8 mM final) elicits an increase in Ca²⁺ !_(i) in theabsence of extracellular Ca²⁺. (b) Pretreatment with ionomycin (1 μM)blocks the response to Mg²⁺. (c). Pretreatment with 5 μM molecule 1799(a mitochondrial uncoupler) is without effect on the response to Mg²⁺.

FIGS. 4a-4c are graphical representations showing preferentialinhibitory effects of a low concentration of Gd³⁺ on steady-stateincreases in Ca²⁺ !_(i) and that a high concentration of Gd³⁺ elicits atransient increase in Ca²⁺ !_(i) in bovine parathyroid cells. Top panel:Control. Initial concentration of extracellular Ca²⁺ was 0.5 mM and wasincreased by 0.5 mM at each of the arrowheads. Middle panel: Gd³⁺ (5 μM)blocks steady-state, but not transient increases in Ca²⁺ !_(i) elicitedby extracellular Ca²⁺. Lower panel: Gd⁺ (50 μM) elicits a transientincrease in Ca²⁺ !_(i) and abolishes both transient and sustainedresponses to extracellular Ca²⁺. In the middle and lower panels, justenough EGTA was added to chelate preferentially Gd³⁺ : the block of Ca²⁺influx is removed and Ca²⁺ !_(i) rises promptly.

FIGS. 5a-5c are graphical representations showing that the effects ofphorbol myristate acetate (PMA) on Ca²⁺ !_(i), IP₃ formation, and PTHsecretion are overcome by increasing concentrations of extracellularCa^(m+) in bovine parathyroid cells. For each variable, there is a shiftto the right in the concentration-response curve for extracellular Ca²⁺.The concentration-response curves vary sigmoidally as Ca²⁺ ! increaseslinearly. The open circles refer to no PMA. The closed circles refer to100 nM PMA.

FIG. 6 is a graphical representation showing that increases in Ca²⁺!_(i) elicited by spermine are progressively d&pressed by increasingCa²⁺ ! in bovine parathyroid cells. Spermine (200 μM) was added at thetime shown by arrowheads. In this and all subsequent figures, thenumbers accompanying the traces are Ca²⁺ !_(i) in nM.

FIG. 7 is a graphical representation showing that spermine mobilizesintracellular Ca²⁺ in bovine parathyroid cells. EGTA was added to reduceCa²⁺ ! to <1 μM before the addition of spermine (200 μM) as indicated(left trace). Pretreatment with ionomycin (1 μM) blocks the response tospermine (right trace).

FIGS. 8a and 8b are graphical representations showing that spermineincreases Ca²⁺ ! and inhibits PTH secretion in bovine parathyroid cellssimilarly to extracellular Ca²⁺. The data points for the spermine doseconcentration-response curves are the means of two experiments.

FIGS. 9a-9c are graphical representations showing the contrastingeffects of PMA on responses to extracellular Ca²⁺ and on responses toATPγS in bovine parathyroid cells. Left panel: Theconcentration-response curve for extracellular Ca²⁺ -induced inhibitionof cyclic AMP formation is shifted to the right by PMA (100 nM). Middlepanel: PMA does not affect the ability of ATPγS to increase Ca²⁺ !_(i).The concentration-response curve to ATPγS shows classical sigmoidalbehavior as a function of the log concentration, in contrast toextracellular divalent cations.

FIGS. 10a-10c are graphical representations showing mobilization ofintracellular Ca²⁺ in human parathyroid cells evoked by extracellularMg²⁺. Cells were obtained from an adenoma and bathed in buffercontaining 0.5 mM extracellular Ca²⁺. (a) Transient and sustainedincreases in Ca²⁺ !_(i) elicited by extracellular Mg²⁺ (10 mM, final)shows that sustained increases are not affected by nimodipine (1 μM) butare depressed by La³⁺ (1 μM) and return promptly when La³⁺ isselectively chelated by a low concentration of EGTA (50 μM). (b) La³⁺ (1μM) blocks the sustained, but not the transient increase in Ca²⁺ !_(i)elicited by extracellular Mg²⁺. (c) Cytosolic Ca²⁺ transients elicitedby extracellular Mg²⁺ persist in the absence of extracellular Ca²⁺.

FIGS. 11a-11i are graphical representations showing mobilization ofintracellular Ca²⁺ evoked by neomycin or protamine in bovine parathyroidcells. In all traces, the initial Ca²⁺ ! and Mg²⁺ ! was 0.5 and 1 mM,respectively. In traces (a) and (b), the Ca²⁺ and Mg²⁺ concentrationswere increased to 2 and 8mM, from 0.5 and 1 mM, respectively. In theother traces, (c) through (i) neomycin B (30 μM) or protamine (1 μg/ml)were added as indicated. La³⁺ (1 μM), EGTA (1 mM), or ionomycin (100 nM)were added as indicated. Each trace is representative of the patternseen in 5 or more trials using at least 3 different cell preparations.Bar=1 minute.

FIG. 12 is a graphical representation showing that neomycin B blockstransient, but does not block steady-state increases in Ca²⁺ !_(i)elicited by extracellular Ca²⁺ in bovine parathyroid cells. Leftcontrol: Ca²⁺ ! was initially 0.5 mM and was increased in 0.5mMincrements at each of the open arrowheads before the addition ofneomycin B (30 μM). Right: Neomycin B (30 μM) was added before Ca²⁺ !.Bar=1 minute. FIGS. 13a and 13b are graphical representations showingthat neomycin B or protamine inhibit PTH secretion at concentrationswhich evoked increases in Ca²⁺ !_(i) in bovine parathyroid cells. Cellswere incubated with the indicated concentrations of organic polycationfor 30 minutes in the presence of 0.5 mM extracellular Ca²⁺. Bovinecells were used in the experiments with protamine and human (adenoma)parathyroid cells were used in the experiments with neomycin B. Eachpoint is the mean ±SEM of 3 experiments. Circles refer to PTH levels inthe presence of 0.5 mM extracellular Ca²⁺ in the presence (closedcircles) and absence (open circles) of neomycin B (FIG. 13a) orprotamine (FIG. 13b). Diamonds refer to Ca²⁺ !_(i) levels in thepresence of 0.5 mM extracellular Ca²⁺ in the presence (closed diamonds)and absence (open diamond) of neomycin B (FIG. 13a) or protamine (FIG.13b). The open square refers to PTH secretion in the presence of 2 mMextracellular Ca²⁺.

FIG. 14 is a graphical representation showing the preferentialinhibitory effects of PMA on cytosolic Ca²⁺ transients elicited byspermine in bovine parathyroid cells. Initial Ca²⁺ ! was 0.5 mM; PMA(100 nM), spermine (200 μM) or ATP (50 μM) were added as indicated.Bar=1 minute.

FIGS. 15a and 15b are graphical representations showing that PMA shiftsto the right the concentration-response curves for extracellular Ca²⁺ -and neomycin B-induced increases in Ca²⁺ !_(i) in bovine parathyroidcells. Cells were either untreated (open circles) or pretreated with 100nM PMA for 1 minute (closed circles) before increasing Ca²⁺ ! or beforeadding neomycin B as indicated. Each point is the mean ±SEM of 3 to 5experiments.

FIGS. 16a and 16b are graphical representations showing that PMA shiftsto the right the concentration-response curves for extracellular Ca²⁺ -and spermine-induced inhibition of PTH secretion in bovine parathyroidcells. Cells were incubated with the indicated Ca²⁺ ! and spermine for30 minutes in the presence (closed circles) or absence (open circles) of100 nM. PMA. Each point is the mean ±SEM of 3 experiments.

FIG. 17 is a graphical representation showing that protamine increasesthe formation of inositol phosphates in bovine parathyroid cells.Parathyroid cells were incubated overnight in culture media containing 4μCi/ml 3H-myo-inositol, washed, and incubated with the indicatedconcentration of protamine at 37° C. After 30 seconds, the reaction wasterminated by the addition of CHCl₃ :MeOH:HCl and Ip₁ (circles) and IP₃(triangles) separated by anion exchange chromatography. Each point isthe mean of 2 experiments, each performed in triplicate.

FIGS. 18a and 18b are graphical representations showing that PMAdepresses the formation of IP₁ evoked by extracellular Ca²⁺ or sperminein bovine parathyroid cells. 3M-Myo-inositol-labeled cells were exposedto the indicated Ca²⁺ !_(i) or spermine for 30 seconds beforeterminating the reaction and determining IP₁ by anion exchangechromatography. Hatched columns: Cells were pretreated with PMA (100 nM)for 5 minutes before increasing Ca²⁺ !_(i) or adding spermine. Eachvalue is the mean of 2 experiments, each performed in triplicate.

FIG. 19 is a graphical representation showing transient and sustainedincreases in Ca²⁺ !_(i) elicited by neomycin B in human (adenoma)parathyroid cells. Extracellular Ca²⁺ was 0.5 mM. (a) The sustainedincrease in Ca²⁺ !_(i) elicited by neomycin B (10 μM) was depressed byLa³⁺ (1 μM). (b) The transient increase in Ca²⁺ !_(i) evoked by neomycinB (10 μM) was unaffected by La³⁺ (1 μM). (c) Transient increases in Ca²⁺!_(i) persisted in the absence of extracellular Ca²⁺ (1 mM of EGTA and10 μM of neomycin B).

FIGS. 20a and 20b are graphical representations showing that neomycin Bevokes oscillating increases the Cl⁻ current in Xenopus oocytesexpressing the calcium receptor. Upper trace from an oocyte three daysafter injection with human (hyperplastic) parathyroid cell poly(A).sup.±-mRNA. Lower trace from an oocyte injected with water. Neomycin B failedto elicit a response in five water-injected oocytes and carbacholelicited a response in one, which is shown. In both traces, the holdingpotential was -76 mV.

FIG. 21 is a graphical representation showing that neomycin B fails toaffect basal or evoked increases in C-cells. Control, left trace:fura-2-loaded rMTC 6-23 cells were initially bathed in buffer containing1 mM Ca²⁺ before increasing Ca²⁺ !_(i) to 3 mM. Right trace:pretreatment with 5 mM neomycin B.

FIG. 22 is a graphical representation showing that extracellular Ca²⁺evokes increases in Ca²⁺ !_(i) in rat osteoclasts. Microfluorimetricrecording in a single rat osteoclast loaded with indo-1 and superfusedfor the indicated times (bars) with buffer containing the indicated Ca²⁺!. Normal buffer, superfused between the bars, contained 1 mM Ca²⁺.

FIG. 23 is a graphical representation showing that spermine or neomycinB fail to evoke increases in Ca²⁺ !_(i) in rat osteoclasts. Anindo-1-loaded osteoclast was superfused with the indicated concentrationof spermine or neomycin B (open bars) alone or together with 20 mM Ca²⁺(solid bars).

FIG. 24 is a graphical representation showing the differential effectsof argiotoxin 659 and argiotoxin 636 on Ca²⁺ !_(i) in bovine parathyroidcells (structures shown in FIG. 1e). The initial Ca²⁺ ! was 0.5 mM andwas increased to 1.5 mM where indicated (right trace). Where indicated,argiotoxin 659 (300 μM) or argiotoxin 636 (400 μM) was added.

FIGS. 25a-25c are graphical representations showing that extracellularMg²⁺ or Gd³⁺ evoke oscillatory increases in Cl⁻ current in Xenopusoocytes injected with bovine parathyroid cell poly(A)⁺ -mRNA. In trace(a), the concentration .of extracellular Ca²⁺ was<1 μM and in traces (b)and (c) it was 0.7 mM. Trace (c) shows that extracellular Mg²⁺ fails toelicit a response in an oocyte injected only With the mRNA for thesubstance K receptor, although superfusion with substance K evokes aresponse. Holding potential was -70 to -80 mV.

FIG. 26 is a graphical representation showing that extracellular Ca²⁺elicits oscillatory increases in Cl⁻ current in Xenopus oocytes injectedwith human (hyperplastic) parathyroid tissue poly(A)⁺ -mRNA. The oocytewas tested for responsivity to extracellular Ca²⁺ three days afterinjection of 50 ng poly(A)⁺ -mRNA. Holding potential was -80 mV.

FIG. 27 is a graphical representation showing the mobilization ofintracellular Ca²⁺ in bovine parathyroid cells elicited bybudmunchiamine. Budmunchiamine (300 μM, structure shown in FIG. 1a) wasadded where indicated.

FIGS. 28a and 28b are graphical representations showing that the abilityof molecules to mobilize intracellular Ca²⁺ in cells expressing acalcium receptor is stereospecific. Different cells were tested forresponse to pure stereoisomers and racemic mixtures. HEK 293 cellsstably transfected with a cDNA clone corresponding to pHuPCaR4.0 (toppanel, FIG. 28b), the rat C-cell line 44-2 isolated from a medullarythyroid carcinoma (middle panel, FIG. 28b) and bovine parathyroid cells(FIG. 28a and bottom panel FIG. 28b) were loaded with fura-2 andsuspended in buffer containing 1.0 mM (top and middle panels FIG. 28b)or 0.5 mM extracellular Ca²⁺ (FIG. 28a and bottom panel FIG. 28b).Intracellular Ca²⁺ was monitored using a fluorimeter. Each point on thegraph represents the peak response (highest concentration ofintracellular calcium achieved) to the addition of the indicatedconcentration of the indicated compound. In FIG. 28a, NPS 457 is aracemic mixture containing compound 1B (see FIG. 36a) and thecorresponding S isomer; NPS 447 is R-fendiline; and NPS 448 isS-fendiline.

FIG. 29 is a graphical representation showing effects of La³⁺ on Ca²⁺!_(i) in osteoclasts. A representative trace from a single ratosteoclast loaded with indo-1 is shown. At low concentrations, La³⁺partially blocks increases in Ca^(2+!) _(i) elicited by extracellularCa²⁺.

FIGS. 30a and 30b are graphical representations showing the mobilizationof intracellular Ca²⁺ elicited by extracellular Mn²⁺ in rat osteoclasts.Extracellular Mn²⁺ evokes concentration-dependent increases in Ca²⁺!_(i) (FIG. 30a) that persist in the absence of extracellular Ca²⁺ (FIG.30b).

FIGS. 31a and 31b are graphical representations showing mobilization ofCa²⁺ !_(i) in rat osteoclasts elicited by prenylamine (shown in thefigures as NPS 449). isolated rat osteoclasts loaded with indo-1 weresuperfused with the indicated concentrations of prenylamine in thepresence (FIG. 31a) or absence (FIG. 31b) of 1 mM extracellular CaCl₂.

FIG. 32 is a graphical representation showing the mobilization ofintracellular Ca²⁺ in C-cells evoked by NPS 019 (see FIG. 1a). rMTC 6-23cells were loaded with fura-2 and bathed in buffer containing 0.5 mMCa²⁺ !. Where indicated, NPS 019 was added to a final concentration of10 μM. Representative traces show that the transient increase in Ca²⁺!_(i) elicited by NPS 019 is refractory to inhibition by La³⁺ (middletrace) and persists in the absence of extracellular Ca²⁺ (right trace, 1mM EGTA).

FIG. 33 is a graphical representation showing that fendiline (shown inthe figure as NPS 456) evokes oscillatory increases in Cl⁻ current inXenopus oocytes which have been injected with 50 ng bovine parathyroidcell poly(A)⁺ -mRNA.

FIG. 34 is a graphical representation showing that extracellular Ca²⁺evokes oscillatory increases in Cl⁻ current in Xenopus oocytes whichhave been injected with human osteoclast mRNA. The oocyte was tested forresponsivity to extracellular Ca²⁺ three days after injection of 50 ngof total poly(A)⁺ -mRNA.

FIG. 35 is a graphical representation showing that the parathyroid cellcalcium receptor is encoded by mRNA in a size range of 2.5-3.5 kb.Bovine parathyroid cell poly(A)⁺ -mRNA was size fractionated on glycerolgradients and pooled into ten fractions. Each fraction was injected (50ng/fraction) separately into Xenopus oocytes. After three days; theoocytes were examined for their ability to respond to neomycin B (10 mM)with oscillatory increases in the Cl⁻ current.

FIG. 36 shows the chemical structures of molecules based on the leadstructure diphenylpropyl-α-phenethylamine (fendeline), illustrating afamily of molecules which were synthesized and screened to find theuseful molecules of the invention.

FIGS. 37a and 37b are graphical representations showing that NPS 021 isa calcilytic compound that blocks the effects of extracellular Ca²⁺ onCa²⁺ !_(i) in bovine parathyroid cells. Cells were initially bathed inbuffer containing 0.5mM CaCl₂ and, where indicated, the Ca²⁺ ! wasincreased to a final of 2 mM (left trace). The addition of NPS 021 (200μM) caused no change in Ca²⁺ !_(i), but inhibited the increase in Ca²⁺!_(i) elicited by extracellular Ca²⁺ (right trace).

FIG. 38 is a graph showing the in vivo serum Ca²⁺ response to NPSR,S-467 in a test animal (a rat). The dosage is provided as mg of drugper kg weight of the test animal.

FIG. 39 is a graph showing the in vivo PTH response to NPS R,S-467 in atest animal (a rat). The dosage is provided as mg of drug per kg weightof the test animal.

FIG. 40 is a graph showing in vivo serum Ca²⁺ response over the courseof 24 hours to 25mg/kg NPS R,S-467 in a test animal (a rat). The dosageis provided as mg of drug per kg weight of the test animal.

FIG. 41 is a graph showing the in vitro response of Ca²⁺ !_(i) incultured bovine parathyroid cells to different enantiomers of NPS 467.EE refers to the R enantiomer. LE and to the S enantiomer.

FIG. 42 is a graph showing the in vivo response of ionized serum Ca²⁺ inrats to different enantiomers of NPS 467. DE and E refer to the Renantiomer. LE and L refer to the S enantiomer. Native refers to theracemic mixture.

FIG. 43a depicts a reaction scheme for the preparation of fendiline orfendiline analogues or derivatives depicted in FIG. 36. FIG. 43b depictsa reaction scheme for the synthesis of NPS 467.

FIG. 44 depicts a dose-response curve showing that NPS R-467 (NPS-467E)lowers serum ionized calcium in rats when administered orally.

FIG. 45 is a restriction map of BoPCaR 1.

FIG. 46 is a restriction map of the plasmid containing BoPCaR 1,deposited with the ATCC under accession number 75416.

FIGS. 47a-d show the nucleotide sequence corresponding to the ˜5 Kbfragment of BoPCaR 1 and the encoded-for amino acid sequence (SEQ. ID.NO. 1).

FIGS. ˜48a-48d show the nucleotide sequence corresponding to the ˜5 Kbinsert from pHuPCaR 5.2 and the encoded-for amino acid sequence (SEQ.ID. NO. 2).

FIGS. 49a-49c show the nucleotide sequence corresponding to the ˜4 Kbinsert from pHuCaR 4.0 and the encoded-for amino acid sequence (SEQ. ID.NO. 3).

FIGS. 50a-50c show the nucleotide sequence corresponding to the ˜4 Kbinsert of pRakCaR 3A and the encoded-for amino acid sequence (SEQ. ID.NO. 4).

FIG. 51 depicts the ability of NPS R-467 and NPS R-568 to potentiate theresponse of a calcium receptor to submaximal concentrations ofextracellular Ca²⁺, and shift the extracellular Ca²⁺concentration-response curve to the left.

FIG. 52 depicts a reaction scheme for compound 17X.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention features: (1) molecules which can modulate one ormore inorganic ion receptor activities, preferably the molecule canmimic or block an effect of an extracellular ion on a cell having aninorganic ion receptor, more preferably the extracellular ion is Ca²⁺and the effect is on a cell having a calcium receptor; (2) inorganic ionreceptor proteins and fragments thereof, preferably calcium receptorproteins and fragments thereof; (3) nucleic acids encoding inorganic ionreceptor proteins and fragments thereof, preferably calcium receptorproteins and fragments thereof; (4) antibodies and fragments thereof,targeted to inorganic ion receptor proteins, preferably calcium receptorprotein; and (5) uses of such molecules, proteins, nucleic acids andantibodies.

Applicant is the first to demonstrate a Ca²⁺ receptor protein inparathyroid cells, and to pharmacologically differentiate such Ca²⁺receptors in other cells, such as C-cells and osteoclasts. Applicant isalso the first to describe methods by which molecules active at theseCa²⁺ receptors can be identified and used as lead molecules in thediscovery, development, design, modification and/or construction ofuseful calcimimetics or calcilytics which are active at Ca²⁺ receptors.

Publications concerned with the calcium activity, calcium receptorand/or calcium receptor modulating compounds include the following:Brown et al., Nature 366: 574, 1993; Nemeth et al., PCT/US93/01642,International Publication Number WO 94/18959; Nemeth et al.,PCT/US92/07175, International Publication Number WO 93/04373; Shobackand Chen, J. Bone Mineral Res. 9: 293 (1994); and Racke et al., FEBSLett. 333: 132, (1993). These publications are not admitted to be priorart to the claimed invention.

I. CALCIUM RECEPTOR-MODULATING AGENTS

Calcium receptor-modulating agents can mimic or block an effect ofextracellular Ca²⁺ on cell having a calcium receptor. Generic andspecific structures of calcium receptor-modulating agents are providedin the. Summary supra, and in FIGS. 1 and 36. Preferred calciumreceptor-modulating agents are calcimimetics and calcilytics. Theability of molecules to mimic or block an activity of Ca²⁺ at calciumreceptors can be determined using procedures described below. The sametype of procedures can be used to measure the ability of a molecule tomimic or block an activity of other inorganic ions at their respectiveinorganic ion receptors by assaying for specific inorganic ion receptoractivities. Examples of these procedures, and other examples providedherein, are not limiting, in the invention, but merely illustratemethods which are readily used or adapted by those of ordinary skill inthe art.

A. Calcium Receptor

Calcium receptors are present on different cell types and can havedifferent activities in different cell types. The pharmacologicaleffects of the following cells, in response to calcium, is consistentwith the presence of a calcium receptor: parathyroid cell, boneosteoclast, juxtaglomerular kidney cell, proximal tubule kidney cell,distal tubule kidney cell, central nervous system cell, peripheralnervous system cell, cell of the thick ascending limb of Henle's loopand/or collecting duct, keratinocyte in the epidermis, parafollicularcell in the thyroid (C-cell), intestinal cell, trophoblast in theplacenta, platelet, vascular smooth muscle cell, cardiac atrial cell,gastrin-secreting cell, glucagon-secreting cell, kidney mesangial cell,mammary cell, beta cell, fat/adipose cell, immune cell, GI tract cell,skin cell, adrenal cell, pituitary cell, hypothalamic cell and cell ofthe subfornical organ. In addition, the presence of calcium receptors onparathyroid cell, central nervous system cell, peripheral nervous systemcell, cell of the thick ascending limb of Henle's loop and/or collectingduct in the kidney, parafollicular cell in the thyroid (C-cell),intestinal cell, GI tract cell, pituitary cell, hypothalamic cell andcell of the subfornical organ, has been confirmed by physical data.

The calcium receptor on these cell types may be different. It is alsopossible that a cell can have more than one type of calcium receptor.Comparison of calcium receptor activities and amino acid sequences fromdifferent cells indicate that distinct calcium receptor types exist. Forexample, calcium receptors can respond to a variety of di- and trivalentcations. The parathyroid calcium receptor responds to calcium and G³⁺,while osteoclasts respond to divalent cations such as calcium, but donot respond to Gd³⁺. Thus, the parathyroid calcium receptor ispharmacologically distinct from the calcium receptor on the osteoclast.

On the other hand, the nucleic acid sequences encoding calcium receptorspresent in parathyroid cells and C-cells indicate that these receptorshave a very similar amino acid structure. Nevertheless, calcimimeticcompounds exhibit differential pharmacology and regulate differentactivities at parathyroid cells and C-cells. Thus, pharmacologicalproperties of calcium receptors may vary significantly depending uponthe cell type or organ in which they are expressed even though thecalcium receptors may have similar or even identical structures.

Calcium receptors, in general, have a low affinity for extracellularCa²⁺ (apparent K_(d) generally greater than about 0.5 mM). Calciumreceptors may include a free or bound effector mechanism as defined byCooper, Bloom and Roth, "The Biochemical Basis of Neuropharmacology",Ch. 4, and are thus distinct from intracellular calcium receptors, e.g.,calmodulin and the troponins.

Calcium receptors respond to changes in extracellular calcium levels.The exact changes depend on the particular receptor and cell linecontaining the receptor. For example, the in vitro effect of calcium onthe calcium receptor in a parathyroid cell includes the following:

1. An increase in internal calcium. The increase is due to the influx ofexternal calcium and/or to mobilization of internal calcium.Characteristics of the increase in internal calcium include thefollowing:

(a) A rapid (time to peak<5 seconds) and transient increase in Ca²⁺!_(i) that is refractory to inhibition by 1 μM La³⁺ or 1 μM Gd³⁺ and isabolished by pretreatment with ionomycin (in the absence ofextracellular Ca²⁺);

(b) The increase is not inhibited by dihydropyridines;

(c) The transient increase is abolished by pretreatment for 10 minuteswith 10 mM sodium fluoride;

(d) The transient increase is diminished by pretreatment with anactivator of protein kinase C (PKC), such as phorbol myristate acetate(PMA), mezerein or (-)-indolactam V. The overall effect of the proteinkinase C activator is to shift the concentration-response curve ofcalcium to the right without affecting the maximal response; and

(e) Pretreatment with pertussis toxin (100 ng/ml for>4 hours) does notaffect the increase.

2. A rapid (<30 seconds) increase in the formation ofinositol-1,4,5-triphosphate or diacylglycerol. Pretreatment withpertussis toxin (100 ng/ml for>4 hours) does not affect this increase;

3. The inhibition of dopamine- and isoproterenol-stimulated cyclic AMPformation. This effect is blocked by pretreatment with pertussis toxin(100 ng/ml for>4 hours); and

4. The inhibition of PTH secretion. Pretreatment with pertussis toxin(100 ng/ml for>4 hours) does not affect the inhibition in PTH secretion.

Using techniques known in the art, the effect of calcium on othercalcium receptors in different cells can be readily determined. Sucheffects may be similar in regard to the increase in internal calciumobserved in parathyroid cells. However, the effect is expected to differin other aspects, such as causing or inhibiting the release of a hormoneother than parathyroid hormone.

B. Calcimimetics

The ability of molecules to mimic or block the activity of Ca²⁺ atcalcium receptors can be determined using the assays described in thepresent application. For example, calcimimetics possess one or more andpreferably all of the following activities when tested on parathyroidcells in vitro:

1. The molecule causes a rapid (time to peak<5 seconds) and transientincrease in Ca²⁺ !_(i) that is refractory to inhibition by 1 μM La³⁺ or1 μM Gd³⁺. The increase in Ca²⁺ !_(i) persists in the absence ofextracellular Ca²⁺, but is abolished by pretreatment with ionomycin (inthe absence of extracellular Ca²⁺);

2. The molecule potentiates increases in Ca²⁺ !_(i) elicited bysubmaximal concentrations of extracellular Ca²⁺ ;

3. The increase in Ca²⁺ !_(i) elicited by extracellular Ca²⁺ is notinhibited by dihydropyridines;

4. The transient increase in Ca²⁺ !_(i) caused by the molecule isabolished by pretreatment for 10 minutes with 10 mM sodium fluoride;

5. The transient increase in Ca²⁺ !_(i) caused by the molecule isdiminished by pretreatment with an activator of protein kinase C (PKC),such as phorbol myristate acetate (PMA), mezerein or (-)-indolactam V.The overall effect of the protein kinase C activator is to shift theconcentration-response curve of the molecule to the right withoutaffecting the maximal response;

6. The molecule causes a rapid (<30 seconds) increase in the formationof inositol-1,4,5-triphosphate and/or diacylglycerol;

7. The molecule inhibits dopamine- or isoproterenol-stimulated cyclicAMP formation;

8. The molecule inhibits PTH secretion;

9. Pretreatment with pertussis toxin (100 ng/ml for>4 hours) blocks theinhibitory effect of the molecule on cyclic AMP formation, but does noteffect increases in Ca²⁺ !!, inositol-1,4,5-triphosphate, ordiacylglycerol, nor decreases in PTH secretion;

10. The molecule elicits increases in Cl⁻ current in Xenopus oocytesinjected with poly(A)+-enriched mRNA from bovine or human parathyroidcells, but is without effect in Xenopus oocytes injected with water, orliver mRNA; and

11. Similarly, using a cloned calcium receptor from a parathyroid cell,the molecule will elicit a response in Xenopus oocytes injected with thespecific cDNA or mRNA encoding the receptor.

Parallel definitions of molecules mimicking Ca²⁺ activity on othercalcium-responsive cells, preferably at a calcium receptor, are evidentfrom the examples provided herein. Preferably, the agent has one ormore, more preferably all of the following activities: evokes atransient increase in internal calcium, having a duration of less that30 seconds (preferably by mobilizing internal calcium); evokes a rapidincrease in Ca²⁺ !_(i), occurring within thirty seconds; evokes asustained increase (greater than thirty seconds) in Ca²⁺ !_(i)(preferably by causing an influx of external calcium); evokes anincrease in inositol-1,4,5-triphosphate or diacylglycerol levels,preferably within less than 60 seconds; and inhibits dopamine-or-isoproterenol-stimulated cyclic AMP formation.

The transient increase in Ca²⁺ !_(i) is preferably abolished bypretreatment of the cell for ten minutes with 10 mM sodium fluoride, orthe transient increase is diminished by brief pretreatment (not morethan ten minutes) of the cell with an activator of protein kinase C,preferably, phorbol myristate acetate (PMA), mezerein or (-) indolactamV.

C. Calcilytics

The ability of a molecule to block or decrease the activity ofextracellular calcium at a cell surface calcium receptor can bedetermined using standard techniques based on the present disclosure.For example, molecules which block or decrease the effect ofextracellular calcium, when used in reference to a parathyroid cell,possess one or more, and preferably all of the following characteristicswhen tested on parathyroid cells in vitro:

1. The molecule blocks, either partially or completely, the ability ofincreased concentrations of extracellular Ca²⁺ to:

(a) increase Ca²⁺ !_(i),

(b) mobilize intracellular Ca²⁺,

(c) increase the formation of inositol-1,4,5-triphosphate,

(d) decrease dopamine- or isoproterenol-stimulated cyclic AMP formation,and

(e) inhibit PTH secretion;

2. The molecule blocks increases in Cl⁻ current in Xenopus oocytesinjected with poly(A)+-mRNA from bovine or human parathyroid cellselicited by extracellular Ca²⁺ or calcimimetic compounds, but not inXenopus oocytes injected with water or liver mRNA;

3. Similarly, using a cloned calcium receptor from a parathyroid cell,the molecule will block a response in Xenopus oocytes injected with thespecific cDNA, mRNA or cRNA encoding the calcium receptor, elicited byextracellular Ca²⁺ or a calcimimetic compound.

Parallel definitions of molecules blocking Ca²⁺ activity on othercalcium responsive cells, preferably at a calcium receptor, are evidentfrom the examples provided herein.

D. Designing Calcium Receptor-Modulating Agents

Generally, calcium receptor-modulating agents are identified byscreening molecules which are modelled after a molecule shown to have aparticular activity (i.e., a lead molecule). Derivative molecules arereadily designed by standard procedures and tested using the proceduresdescribed herein.

Rational design of calcium receptor-modulating agents involves studyinga molecule known to be calcimimetic or calcilytic and then modifying thestructure of the known molecule. For example, polyamines are potentiallycalcimimetic since spermine mimics the action of Ca²⁺ in several invitro systems. Results show that spermine does indeed cause changes inCa²⁺ !_(i) and PTH secretion reminiscent of those elicited byextracellular di- and trivalent cations (see below). Conversely, Ga³⁺antagonizes the effects of Gd³⁺ on the bovine parathyroid calciumreceptor(s). The experiments outlined below are therefore aimed atdemonstrating that this phenomenology, obtained with spermine, involvesthe same mechanisms used by extracellular Ca²⁺. To do this, the effectsof spermine on a variety of physiological and biochemical parameterswhich characterize activation of the calcium receptor were assessed.Those molecules having similar types of effects, and preferably at agreater magnitude, are useful in this invention and can be discovered byselecting or making molecules having a structure similar to spermine.Once another useful molecule is discovered this selection process can bereadily repeated. The same type of analysis can be preformed usingdifferent lead molecules shown to have desired activity.

For clarity, a specific series of screening protocols to identifymolecules active at a parathyroid cell calcium receptor is describedbelow. Equivalent assays can be used for molecules active at othercalcium receptors or other inorganic ion receptors, or which otherwisemimic or antagonize cellular functions regulated by extracellular Ca²⁺ !at a calcium receptor. These assays exemplify the procedures which areuseful to find molecules, including calcimimetic molecules, of thisinvention. Equivalent procedures can be used to find ionolyticmolecules, including calcilytic molecules, by screening for thosemolecules most antagonistic to the actions of the ion, includingextracellular Ca²⁺. In vitro assays can be used to characterize theselectivity, saturability, and reversibility of these calcimimetics andcalcilytics by standard techniques.

1. Screening Procedures

Various screening procedures can be carried out to assess the ability ofa compound to act as a calcilytic or calcimimetic by measuring itsability to have one or more activities of a calcilytic or calcimimetic.In the case of parathyroid cells, such activities include the effects onintracellular calcium, inositol phosphates, cyclic AMP and PTH.

Measuring Ca²⁺ !_(i) with fura-2 provides a very rapid means ofscreening new organic molecules for activity. In a single afternoon,10-15 compounds (or molecule types) can be examined and their ability tomobilize or inhibit mobilization of intracellular Ca²⁺ can be assessedby a single experimenter. The sensitivity of observed increases in Ca²⁺!_(i) to depression by PMA can also be assessed.

For example,.bovine parathyroid cells loaded with fura-2 are initiallysuspended in buffer containing 0.5 mM CaCl₂. A test substance is addedto the cuvette in a small volume (5-15 μl) and changes in thefluorescence signal are measured. Cumulative increases in theconcentration of the test substance are made in the cuvette until somepredetermined concentration is achieved or no further changes influorescence are noted. If no changes in fluorescence are noted, themolecule is considered inactive and no further testing is performed.

In the initial studies, e.g., with polyamine-type molecules, moleculeswere tested at concentrations as high as 5 or 10 mM. As more potentmolecules became known, the ceiling concentration was lowered. Forexample, newer molecules are tested at concentrations no greater than.500 μM. If no changes in fluorescence are noted at this concentration,the molecule can be considered inactive.

Molecules causing increases in Ca²⁺ !_(i) are subjected to additionaltesting. Two characteristics of a molecule which can be considered inscreening a calcimimetic molecule are the mobilization of intracellularCa²⁺ and sensitivity to PKC activators. Molecules causing themobilization of intracellular Ca²⁺ in a PMA-sensitive manner haveinvariably been found to be calcimimetic molecules and to inhibit PTHsecretion. Sensitivity to PKC activators is measured in cells where PKChas not undergone treatment resulting in persistent activation. Chronicpretreatment with low concentrations of PMA (about 30-100 nM treatmentfor about 24 hours) results in persistent activation of PKC and allowsfor the inhibition of PTH secretion by extracellular Ca²⁺ without anyaccompanying increase in Ca!_(i).

A single preparation of cells can provide data on Ca²⁺ !_(i) cyclic AMPlevels, IP₃ and PTH secretion. A typical procedure is to load cells withfura-2 and then divide the cell suspension in two; most of the cells areused for measurement of Ca²⁺ ! and the remainder are incubated withmolecules to assess their effects on cyclic AMP and PTH secretion.Because of the sensitivity of the radioimmunoassays for cyclic AMP andPTH, both variables can be determined in a single incubation tubecontaining 0.3 ml cell suspension (about 500,000 cells).

Measurements of inositol phosphates are a time-consuming aspect of thescreening. However, ion-exchange columns eluted with chloride (ratherthan formate) provide a very rapid means of screening for IP₃ formation,since rotary evaporation (which takes around 30 hours) is not required.This method allows processing of nearly 100 samples in a singleafternoon by a single experimenter. Those molecules that proveinteresting, as assessed by measurements of Ca²⁺ !_(i), cyclic AMP, IP₃,and PTH, can be subjected to a more rigorous analysis by examiningformation of various inositol phosphates and assessing their isomericform by HPLC.

Additional testing can, if needed, be performed to confirm the abilityof a molecule to act as a calcimimetic prior to its use to inhibit PTHin human cells or test animals. Typically, all the various tests forcalcimimetic or calcilytic activity are not performed. Rather, if amolecule causes the mobilization of intracellular Ca²⁺ in aPMA-sensitive manner, it is advanced to screening on human parathyroidcells. For example, measurements of Ca²⁺ !_(i) are performed todetermine the EC₅₀, and to measure the ability of the molecule toinhibit PTH secretion in human parathyroid cells which have beenobtained from patients undergoing surgery for primary or secondaryhyperparathyroidism. The lower the EC₅₀ or IC₅₀, the more potent themolecule as a calcimimetic or calcilytic.

Calcimimetic and calcilytic molecules affecting PTH secretion are thenpreferably assessed for selectivity, for example, by also examining theeffects of such compounds on Ca²⁺ !_(i) or calcitonin secretion incalcitonin-secreting C-cells such as the rat MTC 6-23 cells.

The following is illustrative of methods useful in these screeningprocedures. Examples of typical results for various test calcimimetic orcalcilytic molecules are provided in FIGS. 2-34.

(a) Parathyroid Cell Preparation

This section describes procedures used to obtain and treat parathyroidcells from calves and humans. Parathyroid glands were obtained fromfreshly slaughtered calves (12-15 weeks old) at a local abattoir andtransported to the laboratory in ice-cold parathyroid cell buffer (PCB)which contains .(mM): NaCl, 126; KCl, 4; MgCl₂, 1; Na-HEPES, 20; pH 7.4;glucose, 5.6, and variable amounts of CaCl₂, e..g., 1.25 mM. Humanparathyroid glands, were obtained from patients undergoing surgicalremoval of parathyroid tissue for primary or uremic hyperparathyroidism(uremic HPT), and were treated similarly to bovine tissue.

Glands were trimmed of excess fat and connective tissue and then mincedwith fine scissors into cubes approximately 2-3 mm on a side.Dissociated parathyroid cells were prepared by collagenase digestion andthen purified by centrifugation in Percoll buffer. The resultantparathyroid cell preparation was essentially devoid of red blood cells,adipocytes, and capillary tissue as assessed by phase contrastmicroscopy and Sudan black B staining. Dissociated and purifiedparathyroid cells were present as small clusters containing 5 to 20cells. Cellular viability, as indexed by exclusion of trypan blue orethidium bromide, was routinely 95%.

Although cells can be used for experimental purposes at this point,physiological responses (e.g., suppressibility of PTH secretion andresting levels of Ca²⁺ !_(i)) should be determined after culturing thecells overnight. Primary culture also has the advantage that cells canbe labeled with isotopes to near isotopic equilibrium, as is necessaryfor studies involving measurements of inositol phosphate metabolism.

After purification on Percoll gradients, cells were washed several timesin a 1:1 mixture of Ham's F12-Dulbecco's modified Eagle's medium (GIBCO)supplemented with 50 μg/ml streptomycin, 100 U/ml penicillin, 5 μg/mlgentamicin and ITS⁺. ITS⁺ is a premixed solution containing insulin,transferrin, selenium, and bovine serum albumin (BSA)-linolenic acid(Collaborative Research, Bedford, Mass.). The cells were thentransferred to plastic flasks (75 or 150 cm² ; Falcon) and incubatedovernight at 37° C. in a humid atmosphere of 5% CO₂. No serum is addedto these overnight cultures, since its presence allows the cells toattach to the plastic, undergo proliferation, and dedifferentiate. Cellscultured under the above conditions were readily removed from the flasksby decanting, and show the same viability as freshly prepared cells.

(b) Measurement of Cytosolic Ca²⁺ in Parathyroid Cells

This section describes procedures used to measure cytosolic Ca²⁺ inparathyroid cells. Purified parathyroid cells were resuspended in 1.25mMCaCl₂ -2% BSA-PCB containing 1 μM fura-2-acetoxymethylester andincubated at 37° C. for 20 minutes. The cells were then pelleted,resuspended in the same buffer, but lacking the ester, and incubated afurther 15 minutes at 37° C. The cells were subsequently washed twicewith PCB containing 0.5 mM CaCl₂ and 0.5% BSA and maintained at roomtemperature (about 20° C.). Immediately before use, the cells werediluted five-fold with prewarmed 0.5mM CaCl₂ -PCB to obtain a final BSAconcentration of 0.1%. The concentration of cells in the cuvette usedfor fluorescence recording was 1-2×10⁶ /ml.

The fluorescence of indicator-loaded cells was measured at 37° C. in aspectrofluorimeter (Biomedical Instrumentation Group, University ofPennsylvania, Philadelphia, Pa.) equipped with a thermostated cuvetteholder and magnetic stirrer using excitation and emission wavelengths of340 and 510 nm, respectively. This fluorescence indicates the level ofcytosolic Ca²⁺. Fluorescence signals were calibrated using digitonin (50μg/ml, final) to obtain maximum fluorescence (F_(max)), and EGTA (10 mM,pH 8.3, final) to obtain minimal fluorescence (F_(min)), and adissociation constant of 224 nM. Leakage of dye is dependent ontemperature and most occurs within the first 2 minutes after warming thecells in the cuvette. Dye leakage increases only very slowly thereafter.To correct the calibration for dye leakage, cells were placed in thecuvette and stirred at 37° C. for 2-3 minutes. The cell suspension wasthen removed, the cells pelleted, and the supernatant returned to aclean cuvette. The supernatant was then treated with digitonin and EGTAto estimate dye leakage, which is typically 10-15% of the total Ca²⁺-dependent fluorescent signal. This estimate was subtracted from theapparent F_(min).

(c) Measurement of Cytosolic Ca²⁺ in C-cells

This section describes procedures used to measure cytosolic Ca²⁺ incells. Neoplastic C-cells derived from a rat medullary thyroid carcinoma(rMTC 6-23) were obtained from American Type Culture Collection (ATCCNo. 1607) and cultured as monolayers in Dulbecco's Modified Eagle'smedium (DMEM) plus 15% horse serum in the absence of antibiotics. Formeasurements of Ca²⁺ !_(i), the cells were harvested with 0.02%EDTA/0.05% trypsin, washed twice with PCB containing 1.25 mM CaCl₂ and0.5% BSA, and loaded with fura-2 as described in section I.D.2(b),supra. Measurements of Ca²⁺ !_(i) were performed as described above withappropriate corrections for dye leakage.

(d) Measurement of Ca²⁺ !_(i) in Rat Osteoclasts

This section describes techniques used to measure Ca²⁺ !_(i) in ratosteoclasts. Osteoclasts were obtained from 1-2 day old Sprague-Dawleyrats using aseptic conditions. The rat pups were sacrificed bydecapitation, the hind legs removed, and the femora rapidly freed ofsoft tissue and placed in prewarmed F-12/DMEM media (DMEM containing 10%fetal calf serum and antibiotics (penicillin-streptomycin-gentamicin;100 U/ml-100 μg/ml-100 μg/ml)). The bones from two pups were cutlengthwise and placed in 1 ml culture medium.. Bone cells were obtainedby gentle trituration of the bone fragments with a plastic pipet anddiluted with culture medium. The bone fragments were allowed to settleand equal portions. (about 1 ml) of the medium transferred to a 6-wellculture plate containing 25-mm glass coverslips. The cells were allowedto settle for 1 hour at. 37° C. in a humidified 5% CO₂ -air atmosphere.The coverslips were then washed 3 times with fresh media to removenonadherent cells. Measurements of Ca²⁺ !_(i) in osteoclasts wereperformed within 6-8 hours of removing nonadherent cells.

Cells attached to the coverslip were loaded with indo-1 by incubationwith 5 μM indo-1 acetoxymethylester/0.01% Pluronic F28 for 30 minutes at37° C. in F-12/DMEM lacking serum and containing instead 0.5% BSA. Thecoverslips were subsequently washed and incubated an additional 15minutes at 37° C. in F-12/DMEM lacking the acetoxyester before beingtransferred to a superfusion chamber mounted on the stage of a NikonDiaphot inverted microscope equipped for microfluorimetry. Osteoclastswere easily identified by their large size and presence of multiplenuclei. The cells were superfused with buffer (typically PCB containing0.1% BSA and 1 mM Ca²⁺) at 1 ml/min with or without .test substance. Thefluorescence emitted by excitation at 340 nm was directed through thevideo port of the microscope onto a 440 nm dichroic mirror andfluorescence intensity at 495 and 405 nm collected by photomultipliertubes. The outputs from the photomultiplier tubes were amplified,digitized, and stored in an 80386 PC. Ratios of fluorescence intensitywere used to estimate Ca²⁺ !_(i).

(e) Measuring Ca²⁺ !_(i) in Oocytes

Additional studies used Xenopus oocytes injected with mRNA from bovineor human parathyroid cells and measured Cl⁻ current as an indirect meansof monitoring increases in Ca²⁺ !_(i). The following is an example ofsuch studies used to test the effect of neomycin.

Oocytes were injected with poly(A)+-enriched mRNA from human parathyroidtissue (hyperplastic glands from a case of secondary HPT). After 3 days,the oocytes were tested for their response to neomycin. Neomycin Bevoked oscillatory increases in the Cl⁻ current which ceased uponsuperfusion with drug-free saline (see FIG. 20). Responses to neomycin Bwere observed at concentrations between 100 μM and 10 mM.

To ensure that the response evoked by neomycin B was contingent uponinjection of parathyroid mRNA, the effect of neomycin B on currents inwater-injected oocytes was determined. In each of five oocytes examined,neomycin B (10 mM) failed to cause any change in the current.

About 40% of oocytes are known to respond to carbachol, an effectmediated by an endogenous muscarinic receptor. In five oocytes examinedone showed inward currents in response to carbachol and this is shown inthe lower trace of FIG. 20. Thus, in cells expressing a muscarinicreceptor coupled to increases in Ca²⁺ !_(i) and Cl⁻ current, neomycin Bfails to evoke a response. This shows that the response to neomycin Bdepends on expression of a specific protein encoded by parathyroid cellmRNA. It strongly suggests that in intact cells, neomycin B actsdirectly on the calcium receptor to alter parathyroid cell function.

(f) Measurement of PTH Secretion

In most experiments, cells loaded with fura-2 were also used in studiesof PTH secretion. Loading parathyroid cells with fura-2 does not changetheir PTH secretory response to extracellular Ca²⁺.

PTH secretion was measured by first suspending cells in PCB containing0.5 mM CaCl₂ and 0.1% BSA. Incubations were performed in plastic tubes(Falcon 2058) containing 0.3 ml of the cell suspension with or withoutsmall volumes of CaCl₂ and/or organic polycations. After incubation at37° C. for various times (typically 30 minutes), the tubes were placedon ice and the cells pelleted at 2° C. Samples of the supernatant werebrought to pH 4.5 with acetic acid and stored at -70° C. This protocolwas used for both bovine and human parathyroid cells.

For bovine cells, the amount of PTH in sample supernatants wasdetermined by a homologous radioimmunoassay using GW-1 antibody or itsequivalent at a final dilution of 1/45,000. ¹²⁵ I-PTH (65-84; INCSTAR,Stillwater, Minn.) was used as tracer and fractions separated bydextran-activated charcoal. Counting of samples and data reduction wereperformed on a Packard Cobra 5005 gamma counter.

For human cells, a commercially available radioimmunoassay kit (INS-PTH;Nichols Institute, Los Angeles, Calif.) which recognizes intact andN-terminal human PTH was used because GW-1 antibody recognizes human PTHpoorly.

(g) Measurement of cyclic AMP

This section describes measuring cyclic AMP levels. Cells were incubatedas above for PTH secretion studies and at the end of the incubation, a0.15-ml sample was taken and transferred to 0.85 ml of hot (70° C.)water and heated at this temperature for 5-10 minutes. The tubes weresubsequently frozen and thawed several times and the cellular debrissedimented by centrifugation. Portions of the supernatant wereacetylated and cyclic AMP concentrations determined by radioimmunoassay.

(h) Measurement of Inositol Phosphate Formation

This section describes procedures measuring inositol phosphateformation. Membrane phospholipids were labeled by incubating parathyroidcells with 4 μCi/ml ³ H-myo-inositol for 20-24 hours. Cells were thenwashed and resuspended in PCB containing 0.5 mM CaCl₂ and 0.1% BSA.Incubations were performed in microfuge tubes in the absence or presenceof various concentrations of organic polycation for different times.Reactions were terminated by the addition of 1 mlchloroform-methanol-12N HCl (200:100:1; v/v/v). Aqueous phytic acidhydrolysate (200 μl; 25 μg phosphate/tube). The tubes were centrifugedand 600 μl of the aqueous phase was diluted into 10 ml water.

Inositol phosphates were separated by ion-exchange chromatography usingAG1-X8 in either the chloride- or formate-form. When only IP₃ levelswere to be determined, the chloride-form was used, whereas the formateform was used to resolve the major inositol phosphates (IP₃, IP₂, andIP₁). For determination of just IP₃, the diluted sample was applied tothe chloride-form column and the column was washed with 10 ml 30 mM HClfollowed by 6 ml 90 mM HCl and the IP₃ was eluted with 3 ml 500 mM HCl.The last eluate was diluted and counted. For determination of all majorinositol phosphates, the diluted sample was applied to the formate-formcolumn and IP₁, IP₂, and IP₃ eluted sequentially by increasingconcentrations of formate buffer. The eluted samples from the formatecolumns were rotary evaporated, the residues brought up in cocktail, andcounted.

The isomeric forms of IP₃ were evaluated by HPLC. The reactions wereterminated by the addition of 1 ml 0.45M perchloric acid and stored onice for 10 minutes. Following centrifugation, the supernatant wasadjusted to pH 7-8 with NaHCO₃. The extract was then applied to aPartisil SAX anion-exchange column and eluted with a linear gradient ofammonium formate. The various fractions were then desalted with Dowexfollowed by rotary evaporation prior to liquid scintillation counting ina Packard Tri-carb 1500 LSC.

For all inositol phosphate separation methods, appropriate controlsusing authentic standards were used to determine if organic polycationsinterfered with the separation. If so, the samples were treated withcation-exchange resin to remove the offending molecule prior toseparation of inositol phosphates.

2. Use of Lead Molecules

By systematically measuring the ability of a lead molecule to mimic orantagonize the effect of extracellular Ca²⁺, the importance of differentfunctional groups for calcimimetics and calcilytics were identified. Ofthe molecules tested, some are suitable as drug candidates while othersare not necessarily suitable as drug candidates. The suitability of amolecule as a drug candidate depends on factors such as efficacy andtoxicity. Such factors can be evaluated using standard techniques. Thus,lead molecules can be used to demonstrate that the hypothesis underlyingcalcium receptor-based therapies is correct and to determine thestructural features that enable the calcium receptor-modulating agentsto act on the calcium receptor and, thereby, to obtain other moleculesuseful in this invention.

Examples of molecules useful as calcimimetics include branched or cyclicpolyamines, positively charged polyamino acids, and arylalkylamines. Inaddition, other positively charged organic molecules, includingnaturally occurring molecules and their analogues, are usefulcalcimimetics. These naturally occurring molecules and their analoguespreferably have positive charge-to-mass ratios that correlate with thoseratios for the molecules exemplified herein. (Examples include materialisolated from marine species, arthropod venoms, terrestrial plants andfermentation broths derived from bacteria and fungi.) It is contemplatedthat one group of preferred naturally occurring molecules and analoguesuseful as calcimimetics will have a ratio of positive charge: molecularweight (in daltons) from about 1:40 to 1:200, preferably from about 1:40to 1:100.

FIG. 36 provides additional examples of molecules expected to act aseither calcilytics or calcimimetics based upon their structure. Ingeneral these molecules were synthesized based on the lead molecule,fendiline, and tested to determine their respective EC₅₀ or IC₅₀ values.Studies of stereoisomers, such as NPS 447 (R-fendiline) and NPS 448(S-fendiline), have revealed stereospecific effects of molecularstructure. The most active compounds tested to date are designated NPSR-467, NPS R-568, compound 8J, compound 8U, compound 9R, compound 11X,compound 12U, compound 12V, compound 12Z, compound 14U, compound 17M,compound 17P and compound 17X (see Table, infra). These compounds allhave EC₅₀ values of less than 5 μM at the parathyroid cell calciumreceptor.

The examples described herein demonstrate the general design ofmolecules useful as ionomimetics and ionolytics, preferably,calcimimetics and calcilytics. The examples also describe screeningprocedures to obtain additional molecules, such as the screening ofnatural product libraries. Using these procedures, those of ordinaryskill in the art can identify other useful ionomimetics and ionolytics,preferably calcimimetics and calcilytics.

(a) Functional Groups

This section describes useful functional groups for conferring increasedmimetic or lytic activity and analytical procedures which can be used toidentify different functional groups from lead molecules. Analysis oflead molecules have identified useful functional groups such as aromaticgroups, stereospecificity (R-isomer) and preferred charge-to-moleculeweight ratios. The described analytic steps and analogous analyses canbe conducted on other lead molecules to obtain calciumreceptor-modulating agents of increasing activity.

A factor examined earlier on was the charge-to-size ratio of a calciumreceptor-modulating agent. Initial results of testing the correlationbetween net positive charge and potency in mobilizing intracellular Ca²⁺in parathyroid cells revealed that protamine (+21; EC₅₀ =40 nM) was moreeffective than neomycin B (+6; EC₅₀ =20 μM in human parathyroid cellsand 40 μM in bovine parathyroid cells), which was more effective thanspermine (+4; EC₅₀ =150 μM).

These results raised the question of whether positive charge alonedetermines potency, or if there are other structural featurescontributing to activity on the calcium receptor. This was important todetermine at the outset because of its impact on the view that thecalcium receptor can be targeted with effective and specific therapeuticmolecules. Thus, a variety of other organic polycations related toneomycin B and spermine were studied to determine the relationshipbetween the net positive charge of a molecule and its potency tomobilize intracellular Ca²⁺.

The first series of molecules studied were the aminoglycosides. Theability of these molecules to mobilize intracellular Ca²⁺ was determinedin bovine parathyroid cells. The rank order of potency for elicitingcytosolic Ca²⁺ transients was neomycin B (EC₅₀ =20 or 40 μM)>gentamicin(150 μM)>bekanamycin (200 μM)>streptomycin (600 μM). Kanamycin andlincomycin were without effect when tested at a concentration of 500 μM.The net positive charge on these aminoglycosides at pH 7.3 is neomycin B(+6) gentamicin (+5)=bekanamycin (+5)>kanamycin (average+4.5)streptomycin (+3)>lincomycin (+1). Thus, within the aminoglycosideseries there is some correlation between net positive charge and calciumreceptor-modulating activity. However, the correlation is not absoluteas illustrated by kanamycin, which would be predicted to be more potentthan streptomycin, having no activity.

Testing of Various polyamines revealed additional and more markeddiscrepancies between net positive charge and potency. Three structuralclasses of polyamines were examined: (1) straight-chain, (2)branched-chain, and (3) cyclic. The structures of the polyamines testedare provided in FIG. 1. Amongst the straight-chain polyamines, spermine(+4; EC₅₀ =150 μM) was more potent than pentaethylenehexamine (+6; EC₅₀=500 μM) and tetraethylenepentamine (+5; EC₅₀ =2.5 mM), even though thelatter molecules have a greater net positive charge.

Branched-chain polyamines having different numbers of secondary andprimary amino groups and, thus, varying in net positive charge weresynthesized and tested. Two of these molecules, NPS 381 and NPS 382,were examined for effects on Ca²⁺ !_(i) in bovine parathyroid cells. NPS382 (+8; EC₅₀ =50 μM) was about twice as potent as NPS 381 (+10; EC₅₀=100 μM), even though it contains two fewer positive charges.

A similar discrepancy between positive charge and potency was noted inexperiments with cyclic polyamines. For example, hexacyclen (+6; EC₅₀=20 μM) was more potent than NPS 383 (+8; EC₅₀ =150 μM). The resultsobtained with these polyamines show that positive charge is not the solefactor contributing to potency.

Additional studies provided insights into other structural features ofmolecules that impart activity on the parathyroid cell Calcium receptor.One of the structurally important features is the intramoleculardistance between the nitrogens (which carry the positive charge).Spermine is 50-fold more potent than triethylenetetramine (EC₅₀ =8 mM)in evoking increases in Ca²⁺ !_(i) in bovine parathyroid cells, yet bothmolecules carry a net positive charge of +4. The only difference instructure between these two polyamines is the number of methylenesseparating the nitrogens: in spermine it is 3-4-3 whereas intriethylenetetramine it is 2-2-2. This seemingly minor change in thespacing between nitrogens has profound implications for potency andsuggests that the conformational relationships of nitrogens within themolecule are important.

Studies with hexacyclen and pentaethylenehexamine further demonstratedthe importance of the conformational relationship. The former moleculeis simply the cyclic analog of the latter and contains the same numberof methylenes between all nitrogens, yet the presence of the ringstructure increases potency 25-fold. These results indicate thatpositive charge per se is not the critical factor determining theactivity of an organic molecule on the calcium receptor.

Another series of experiments revealed the importance of aromatic groupsin determining activity on the calcium receptor. The initial resultswere obtained using two arylalkyl polyamines isolated from the venom ofthe spider Argiope lobata. These molecules, argiotoxin 636 andargiotoxin 659, have identical polycationic portions linked to differentaromatic groups (FIG. 1e). Argiotoxin 659 evoked transient increases inCa²⁺ !_(i) in bovine parathyroid cells when tested at concentrations of100 to 300 μM. In contrast, argiotoxin 636 had no effect when tested atsimilar concentrations (FIG. 24). The only difference in structurebetween these two arylalkyl polyamines is in the aromatic portion of themolecules: argiotoxin 659 contains a hydroxyindole moiety whereasargiotoxin 636 contains a dihydroxyphenyl group. The net positive chargeon these two arylalkyl polyamines is the same (+4), so their differentpotencies results from the different aromatic groups. This findingsfurther demonstrates that net positive charge alone does not determinepotency and that aromatic groups contribute significantly to the abilityof molecules to activate the calcium receptor.

Substitutions on aromatic rings also effect calcium receptor-modulatingactivity. Agatoxin 489 (NPS 017) and Agatoxin 505 (NPS 015) both causethe mobilization of intracellular Ca²⁺ in parathyroid cells with EC₅₀ 'sof 6 and 22 μM, respectively. The only difference between the structuresof these molecules is a hydroxyl group on the indole moiety (FIG. 1f).

Thus, the structural features to be varied systematically from leadmolecules described herein include the following: (1) net positivecharge; (2) number of methylenes separating nitrogens; (3) cyclicversions of molecules, for example polyamines with and without changesin methylene spacing and net positive charge; and (4) the structure andlocation of aromatic groups.

A variety of arylalkyl polyamines can be isolated from the venoms ofwasps and spiders. Additionally, analogous synthetic molecules can beprepared by the coupling of commercially available aromatic moieties tothe argiotoxin polyamine moiety. The argiotoxin polyamine moiety can bereadily coupled to any aromatic moiety containing a carboxylic acid.

One of ordinary skill in the art can readily obtain and systematicallyscreen the hydroxy and methoxy derivatives of phenylacetic acid andbenzoic acid as well as the hydroxyindoleacetic acid series using thetechniques described herein. Analogues containing heteroaromaticfunctionalities can also be prepared and assessed for activity.Comparisons of potency and efficacy among molecules having differentfunctional groups will reveal the optimal structure and location of thearomatic group at a constant positive charge.

(b) Testing of Natural Products

Testing of natural products and product libraries can be carried out toidentify functional groups and to test molecules having particularfunctional groups. Screening of natural products selected on the basisof the structural information can be readily performed using thestructure-function relationships established by the testing of leadmolecules. For example, molecules can be selected on the basis ofwell-established chemotaxonomic principles using appropriate data bases,such as Napralert, to obtain pools of molecules having desiredfunctional groups. For example, macrocyclic polyamine alkaloids derivedfrom papilionoid legumes related to Albizia, such as Pithecolobium, andother plant-derived molecules can be screened.

The results obtained with budmunchiamine A illustrate the predictivepower of the structure-activity studies and the novel structuralinformation to be gained by testing natural products. One of thestructural variations on the polyamine motif that seems to increasepotency is the presence of the cyclic version of the straight-chainparent molecule. Budmunchiamine A, isolated from the plant Albiziaamara, is a cyclic derivative of spermine (FIG. 1a). The addition ofbudmunchiamine A to bovine parathyroid cells caused a rapid andtransient increase in Ca²⁺ !_(i) that persisted in the absence ofextracellular Ca²⁺ and was blunted by pretreatment with PMA. Ittherefore causes the mobilization of intracellular Ca²⁺ in parathyroidcells, probably by acting on the calcium receptor. It is aboutequipotent with spermine (EC₅₀ about 200 μM), yet carries one lesspositive charge (+3) than does spermine.

3. Polyamines

Preferred polyamines useful as calcimimetics in this invention may beeither branched or cyclic. Branched or cyclic polyamines potentiallyhave higher calcimimetic activity than their straight-chain analogues.That is, branched or cyclic polyamines tend to have a lower EC₅₀ thantheir corresponding linear polyamines with the same effective charge atphysiological pH (see Table 1).

                  TABLE 1                                                         ______________________________________                                                            Net (+)                                                   Molecule            Charge  EC.sub.50 (μM)                                 ______________________________________                                        Neomycin            +6      20 or 40                                          Hexacyclen          +6      20                                                NPS 382             +8      50                                                NPS 381              +10    100                                               NPS 383             +8      150                                               Gentamicin          +5      150                                               Spermine            +4      150                                               Bekanamycin         +5      200                                               Argiotoxin-659      +4      300                                               Pentaethylenehexamine (PEHA)                                                                      +6      500                                               Streptomycin        +3      600                                               Spermidine          +3      2000                                              Tetraethylenepentamine (TEPA)                                                                     +5      2500                                              1,12-diaminododecane (DADD)                                                                       +2      3000                                              Triethylenetramine (TETA)                                                                         +4      8000                                              ______________________________________                                    

"Branched polyamines" as used herein refers to a chain moleculeconsisting of short alkyl bridges or alkyl groups joined together byamino linkages, and also containing points at which the chain branches.These "branch points" can be located at either a carbon atom or anitrogen atom, preferably at a nitrogen atom. A nitrogen atom branchpoint is typically a tertiary amine, but it may also be quaternary. Abranched polyamine may have 1 to 20 branch points, preferably 1 to 10branch points.

Generally, the alkyl bridges and alkyl branches in a branched polyamineare from 1 to 50 carbon atoms in length, preferably 1-15, morepreferably from 2 to 6 carbon atoms. The alkyl branches may also beinterrupted by one or more heteroatoms (nitrogen, oxygen or sulfur) orsubstituted with functional groups such as: halo, including fluoro,chloro, bromo, or iodo; hydroxy; nitro; acyloxy (R'COO--), acylamido(R'CONH--), or alkoxy (--OR'), where R' may contain from 1 to 4 carbonatoms. The alkyl branches may also be substituted with groups that arepositively charged at physiological pH, such as amino or guanidino.These functional substituents may add or change physical properties suchas solubility to increase activity, delivery or bioavailability of themolecules.

The branched polyamines may have three or more chain and branchtermination points. These termination points may be methyl groups oramino groups, preferably amino groups.

A preferred group of branched polyamines have the formula:

    H.sub.2 N--(CH.sub.2).sub.j --(NR.sub.i --(CH.sub.2).sub.j).sub.k --NH.sub.2

where k is an integer from 1 to 10;

each j is the same or different and is an integer from 2 to 20;

each R_(i) is the same or different and is selected from the groupconsisting of hydrogen and --(CH₂)_(j) --NH₂, where j is as definedabove; and

at least one R_(i) is not hydrogen.

Particularly preferred branched polyamines of this invention are themolecules N¹, N¹, N⁵, N¹⁰, N¹⁴, N¹⁴ -hexakis-(3-aminopropyl) spermineand N¹, N¹, N⁵, N¹⁴, N¹⁴ -tetrakis-(3-aminopropyl)spermine referred toas NPS 381 and NPS 382, respectively, in FIGS. 1a and 1f.

"Cyclic polyamines" refers to heterocycles containing two or moreheteroatoms (nitrogen, oxygen or sulfur), at least two of which arenitrogen atoms. The heterocycles are generally from about 6 to about 20atoms in circumference, preferably from about 10 to about 18 atoms incircumference. The nitrogen heteroatoms are separated by 2 to 10 carbonatoms. The heterocycles may also be substituted at the nitrogen siteswith aminoalkyl or aminoaryl groups (NH₂ R--), wherein R is aminoaryl ora lower alkyl of 2 to 6 carbon atoms. Particularly preferred cyclicpolyamines of this invention are shown in FIGS. 1f and 1a as hexacyclen(1,4,7,10,13,16-hexaaza-cyclooctadecane) and NPS 383.

4. Polyamino Acids

"Polyamino acids" refers to polypeptides containing two or more aminoacid residues which are positively charged at physiological pH.Positively charged amino acids include histidine, lysine and arginine.The polyamino acids can vary in length from 2 to 800 amino acids, morepreferably from 20 to 300 amino acids and may consist of a singlerepeating amino acid residue or may have the variety of a naturallyoccurring protein or enzyme. Preferred polyamino acids are polyarginine,polylysine, and poly(argininyl-tyrosine), having 20-300 residues, andprotamine or a protamine analog.

The amino acid residues present in the polyamino acids may be any of thetwenty naturally occurring amino acids, or other alternative residues.Alternative residues include, for example, the ω-amino acids of theformula H₂ N(CH₂)_(n) COOH, where n is from 2 to 6, and other nonpolaramino acids, such as sarcosine, t-butyl alanine, t-butyl glycine,N-methyl isoleucine, norleucine, phenyl glycine, citrulline, methioninesulfoxide, cyclohexyl alanine, and hydroxyproline. Ornithine is anexample of an alternative positively charged amino acid residue. Thepolyamino acids of this invention may also be chemically derivatized byknown methods.

5. Arylalkyl Polyamines

"Arylalkyl polyamines" refers to a class of positively charged naturalproducts derived from arthropod venoms. Preferred arylalkyl polyaminesare philanthotoxin-433, argiotoxin-636, argiotoxin-659, agatoxin 505,agatoxin 489 (FIG. 1), and analogous synthetic molecules modeled afterthese natural products.

6. Arylalkyl Amines

Preferred molecules of the present invention are arylalkyl amines havingstructure I; more preferably having structure III described supra,wherein R₂ is an aryl group, preferably a carbocyclic aryl group such asphenyl or a bicyclic carbocyclic aryl groups such as naphthyl,preferably 1-naphthyl. Especially preferred are R-isomers.

Two examples of arylalkyl amines are NPS 467 and NPS 568. NPS 467 andNPS 568 are analogues. NPS 568 is more potent in causing increases inCa²⁺ !_(i) in bovine and human parathyroid cells than NPS 467. Theeffects of NPS 568 and NPS 467 are stereospecific and it is the R-isomerthat is the more potent enantiomer (see Table 6, infra). NPS R-568 is atpresent the lead calcimimetic compound with selective activity at theparathyroid cell calcium receptor.

NPS R-568 behaves, albeit with greater potency, similarly to NPS R-467.NPS R-568 evokes increases in Ca²⁺ !_(i) in bovine parathyroid cells ina stereospecific manner (see Table 6, infra). NPS R-568 fails to evokeincreases in Ca²⁺ !_(i) in the absence of extracellular Ca²⁺, but itdoes potentiate responses to extracellular Ca²⁺. NPS R-568 shifts theconcentration-response curve for extracellular Ca²⁺ to the left.

The oral administration of NPS R-568 to rats causes a dose-dependentdecrease in the levels of serum Ca²⁺ (ED₅₀ =7 mg/kg). The hypocalcemicresponse elicited by the oral administration of NPS R-568 is rapid inonset and is paralleled by decreases in the levels of serum PTH. Thehypocalcemic response evoked by the oral administration of NPS R-568 isonly marginally affected by prior complete nephrectomy. However, NPSR-568 fails to elicit a hypocalcemic response in parathyroidectomizedrats. NPS R-568 can thus target selectively the parathyroid cell calciumreceptor in vivo and cause an inhibition of PTH secretion. The decreasesin serum levels of PTH together with the resulting hypocalcemia aredesirable therapeutic effects in cases of hyperparathyroidism.

Also preferred are arylalkyl amines having the structure: ##STR5## MorePreferably ##STR6## Alkyl=C₁ -C₆ cyclic, preferably linear, or morepreferably branched hydrocarbon (sp² or preferably sp³ hybridization)Ar=(preferably) phenyl, 1-, or 2-naphthyl

More Preferably ##STR7## Alkyl=C₁ -C₆ cyclic, preferably linear, or morepreferably branched hydrocarbon (sp² or preferably sp³ hybridization).Ar¹ =(preferably) phenyl or 2-naphthyl; Ar² (preferably)=phenyl or1-naphthyl. R¹ =(preferably) methyl, R² =(preferably) H

Most Preferably ##STR8## X=nothing; for example when C (Carbon, see Z=)are sp² or sp¹, or for example when Y=O (Oxygen). Possible combinationsare not limited to these examples.

X=--F, --Cl, --Br, or --I

X=--OR

X=--NR₂ (R's selected independently)

X=--Sa, S(O)R, S(O)₂ R,

X=--ON

X=--NO₂

X=--C(O)R --OC(O)R, --C(O)OR --NRC(O)R, O(O)NR₂, (R's selectedindependently)

R=--H, --C F₃, --CF₂ H, --CFH₂, --OH₂ CF₃, --C₁ -C₁₀ (sp, sp², or sp³carbons, selected independently) alkyl (linear, branched, cyclic system,fused cyclic or bicyclic systems, selected independently) or phenyl.

Ar=any aromatic, heteroaromatic, or heterocyclic system, preferablyphenyl, 1-naphthyl, 2-naphthyl, biphenyl, tetrahydronaphthyl, indanyl,indenyl, fluorenyl, 9,10-dihydranthracenyl, 9,10-dihydrophenanthrenyl,pyrrolyl, furanyl, 1,2,3-triazolyl, 1,2,4-triazolyl, tetrazolyl,imidazolyl, oxazolyl, thiazolyl, pyrazolyl, thiofuranyl, isoxazolyl,pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, 1,2,4-triazinyl,1.3,5-triazinyl, tetrahydrofuranyl, pyrrolidinyl, imidazolinyl,thiazolidinyl, decahydroquinolinyl, decahydroisoquinolinyl, piperidinyl,piperizinyl, morpholinyl, thiomorpholinyl, benzofuranyl,dihydrobenzofuranyl, dihydrobenzopyranyl, benzimadazolyl, indazolyl,tetrahydroquinolinyl, tetrahydroisoquinoline, quinolinyl, isoquinolinyl,benzotriazolyl, carbazolyl, indolyl, indolinyl, phenoxazinyl,phenothiazinyl, α-carbolinyl, β-carbolinyl, acenaphthenyl, oracenaphthylenyl.

Y=--NR, --O, --S, --S(O), --S(O)₂, --C*R, --C*(O), --OC*(O), --C*(O)O,--NRC*(O), C*(O)NR, (*sp² carbon), --OR₂, --CRX, or --CX₂.

m=1 through 7 inclusive (independent).

Z and N together form a piperidinyl, piperazinyl or pyrrolinyl ring.

7. Additional Components

Calcium receptor-modulating agents may be substituted with additionalcomponents. The additional components are used to provide additionalfunctionality to the molecules, apart from the molecules' ability to actas a calcimimetic or calcilytic. These additional components includetargeting components and functionalities such as labels which enhance amolecule's ability to be used in the different applications, such as forscreening for agonists or antagonists of extracellular Ca²⁺ in acompetitive or non-competitive assay format.

For example, an immunoglobulin or a ligand specific for parathyroidcells or a calcium receptor can be used as a target-specific component.The immunoglobulin can be a polyclonal or monoclonal antibody and maycomprise whole antibodies or immunologically reactive fragments of theseantibodies such as F(_(ab')), F(_(ab)), or (F_(ab'))₂.

A wide variety of labeling moieties can be used, includingradioisotopes, chromophores, and fluorescent labels. Radioisotopelabeling in particular can be .readily detected in vivo. Radioisotopesmay be coupled by coordination as cations in the porphyrin system.Useful cations include technetium, gallium, and indium. In thecompositions, the positively charged molecule can be linked to orassociated with a label.

II. SYNTHESIS OF CALCIUM RECEPTOR-MODULATING AGENTS

Different ionomimetics and ionolytics can be synthesized by usingprocedures known in the art and described herein. ionomimetics andionolytics can also be synthesized as described by Bradford CVanWagenen, Steven R Duff, William A. Nelson and Thomas E. D'Ambra inU.S. patent application, entitled "Amine Preparation" herebyincorperated by reference herein.

A. Synthesis of Polyamines

The synthetic methods used to produce polyamines described in thissection are modelled after methods used to construct argiopines 636 and659 and other arylalkyl polyamines derived from spider venoms.Polyamines can be synthesized starting with, for example, diaminoalkanesand simple polyamines such as spermidine or spermine. Strategies for thesynthesis and the modification of polyamines involve using a variety ofamine-protecting groups (e.g., phthalimido, BOC, CBZ, benzyl, andnitrile) which can be selectively removed to construct functionalizedmolecules.

Chain extensions, of the starting material, by 2-4 methylenes weretypically accomplished by alkylation with the correspondingN-(bromoalkyl)phthalimide. A 1:1.2 mixture of amine to thebromoalkylphthalimide was refluxed in acetonitrile in the presence of50% KF on Celite. Chain extensions were also accomplished by alkylationof a given amine with acrylonitrile or ethylacrylate. Reaction progresswas monitored by thin-layer chromatography (TLC) and intermediatespurified on-silica gel using combinations of dichloromethane, methanol,and isopropylamine. Final products were purified by cation exchange(HEMA-SB) and RP-HPLC (Vydac C-18). Purity and structure verificationwere accomplished by ¹ H- and ¹³ C-NMR spectroscopy and high-resolutionmass spectrometry (EI, CI and/or FAB).

Amine-protecting groups, phthalimido, BOC, CBZ, benzyl, and nitrile,were added and later selectively removed to construct functionalizedmolecules. BOC protecting groups were added by treating a primary orsecondary amine (1° or 2°) with di-tert-butyl dicarbonate indichloromethane. Benzyl protecting groups were applied in one of twoways: (1) condensation of a 1° amine with benzaldehyde followed bysodium borohydride reduction or (2) alkylation of a 2° amine withbenzylbromide in the presence of KF.

Deprotection of the different groups was carried out using differentprocedures. Deprotection of the phthalimido functionality wasaccomplished by reduction with hydrazine in refluxing methanol.Deprotection of the BOC functionality was accomplished in anhydrous TFAor concentrated HCl in acetonitrile. Deprotection of benzyl, nitrile,and CBZ protecting functionalities was accomplished by reduction inglacial acetic acid under 55 psi hydrogen in the presence of a catalyticamount of palladium hydroxide on carbon. Nitrile functionalities in thepresence of benzyl and CBZ groups were selectively reduced underhydrogen in the presence of sponge Raney nickel.

Amide linkages were typically prepared by reacting an amine (1° or 2°)with an N-hydroxysuccinimide or p-nitrophenylester of a given acid. Thiswas accomplished directly, in the case of adding cyclic groups, bytreating the amine with dicyclohexylcarbodiimide under diluteconditions.

Specifically, branched polyamines are typically prepared from simplediaminoalkanes of the formula NH₂ --(CH₂)_(n) --NH₂, or simplepolyamines such as spermidine or spermine. One of the two primary(terminal) amines is protected or "masked" with a protecting group suchas BOC (t-butyloxycarbonyl), phthalimido, benzyl, 2-ethylnitrile (theMichael condensation production product of an amine and acrylonitrile),or amide. A typical reaction is the addition of a BOC protecting groupby treatment with di-t-butyl-dicarbonate (BOC anhydride): ##STR9## Themonoprotected product is separated from the unprotected and diprotectedproducts by simple chromatographic or distillation techniques.

The remaining free amine in the monoprotected product is thenselectively alkylated (or acylated) with an alkylating (or acylating)agent. To ensure mono-alkylation, the free amine is partially protectedby condensation with benzaldehyde followed by sodium borohydridereduction to form the N-benzyl derivative: ##STR10## The N-benzylderivative is then reacted with the alkylating agent. A typicalalkylating agent is in an N-(bromoalkyl)phthalimide, which reacts asfollows: ##STR11## For example, N-(bromobutyl)phthalimide is used toextend or branch the chain with four methylene units. Alternatively,reaction with acrylonitrile followed by reduction of the cyano groupwill extend the chain by three methylenes and an amino group.

The protecting groups of the resulting chain-extended molecule can thenbe selectively cleaved to yield a new free amine. For example,trifluoroacetic acid is used to remove a BOC group; catalytichydrogenation is used to reduce a nitrile functionality and remove abenzyl group; and hydrazine is used to remove phthalimido groups asfollows: ##STR12##

The new free amine may be alkylated (or acylated) further as above toincrease the length of the polyamine. This process is repeated until thedesired chain length and number of branches is obtained. In the finalstep, deprotection of the product results in the desired polyamine.However, further modifications may be effected at the protected endprior to deprotection. For example, prior to BOC-deprotection, thepolyamine is acylated with the N-hydroxysuccinimide ester of3,4-dimethoxyphenylacetic acid to yield a diprotected polyamine:##STR13## This ultimately yields an arylalkyl polyamine. The BOC groupcan then be selectively removed with trifluoroacetic acid to expose theother amino terminus which can be extended as above.

Certain branched polyamines may be formed by simultaneously alkylatingor acylating the free primary and secondary amines in a polyamine formedas above. For example, treatment of spermine with excess acrylonitrilefollowed by catalytic reduction yields the following: ##STR14## Cyclicpolyamines may be prepared as above with starting materials such ashexacylen (Aldrich Chem.).

B. Polyamino Acid Synthesis

Polyamino acids can be made using standard techniques such as beingtranslated using recombinant nucleic acid techniques or beingsynthesized using standard solid-phase techniques. Solid-phase synthesisis commenced from the carboxy-terminal end of the peptide using anα-amino protected amino acid. BOC protective groups can be used for allamino groups even through other protective groups are suitable. Forexample, BOC-lys-OH can be esterified to chloromethylated polystyreneresin supports. The polystyrene resin support is preferably a copolymerof styrene with about 0.5 to 2% divinylbenzene as a cross-linking agentwhich causes the polystyrene polymer to be completely insoluble incertain organic solvents. See Stewart et al., Solid-Phase PeptideSynthesis (1969), W. H. Freeman Co., San Francisco; and Merrifield, J.Am. Chem. Soc. (1963) 85:2149-2154. These and other methods of peptidesynthesis are also exemplified by U.S. Pat. Nos. 3,862,925; 3,842,067;3,972,859; and 4,105,602.

The polypeptide synthesis may use manual techniques or be automated. Forexample, synthesis can be carried out using an Applied Biosystems 403APeptide Synthesizer (Foster City, Calif.) or a Biosearch SAM IIautomatic peptide synthesizer (Biosearch, Inc., San Rafael, Calif.),following the instructions provided in the instruction manual suppliedby the manufacturer.

C. Arylalkyl Polyamines

Arylalkyl polyamines such as those shown in FIG. 1 can be obtained fromnatural sources isolated by known techniques, or synthesized asdescribed in Jasys et al., Tetrahedron Lett. 29:6223-6226, (1988);Nason. et al., Tetrahedron Lett. 30:2337-2340, (1989); and Schafer etal., "Polyamine Toxins from Spiders and Wasps," The Alkaloids, vol. 45,p. 1-125, 1994.

D. Arylalkylamines

This section describes general protocol to prepare arylalkylamines suchas fendiline or fendiline analogues as shown in FIG. 36. In a 10-mlround-bottom flask equipped with a magnetic stir bar and rubber septum,1.0 mmole 3,3'-diphenylpropylamine (or primary alkylamine such assubstituted or unsubstituted phenylpropylamine) in 2 ml ethanol wastreated with 1.0 mmole acetophenone (or substituted acetophenone). Twomillimoles MgSO₄ and 1.0 mmole NaCNBH₃ were then added and the solutionwas stirred under a nitrogen atmosphere at room temperature (about 20°C.) for 24 hours. The reaction was poured into 50 ml ether and washed 3times with 1N NaOH and once with brine. The ether layer was dried withanhydrous K₂ CO₃ and reduced in vacuo. The product was then purified bycolumn chromatography or HPLC incorporating a silica stationary phasewith combinations of CH₂ Cl₂ -methanol-isopropylamine (typically 3%methanol and 0.1% isopropylamine in methylene chloride).

A preferred procedure for preparing fendiline or fendiline analogues(such as those depicted in FIG. 36) uses titanium (IV) isopropoxide andwas modified from methods described in J. Org. Chem. 55:2552 (1990). Forthe synthesis of Compound 2M, titanium tetrachloride (method describedin Tetrahedron Lett. 31:5547 (1990)) was used in place of titanium (IV)isopropoxide.

A reaction scheme is depicted in FIG. 43a. In FIG. 43a, R, R' and R"depict appropriately substituted hydrocarbon and aromatic moietiesgroups. Referring to FIG. 43a in a 4-ml vial, 1 mmole of amine (1)(typically a primary amine) and 1 mmole ketone or aldehyde (2)(generally an appropriately substituted acetophenone) are mixed, thentreated with 1.25 mmoles titanium(IV) isopropoxide (3) and allowed tostand with occasional stirring at room temperature for about 30 minutes.Alternatively, a secondary amine may be used in place of (1). Reactionsgiving heavy precipitates or solids can be heated to their melting pointto allow for mixing during the course of the reaction.

The reaction mixture is then treated with 1 ml ethanol containing 1mmole sodium cyanoborohydride (4) and the resulting mixture is allowedto stand at room temperature with occasional, stirring for about 16hours. After this time the reaction is quenched by the addition of about500 μl water. The reaction mixture is then diluted to about 4 ml totalvolume with ethyl ether and then centrifuged. The upper organic phase isremoved and reduced on a rotavapor. The resulting product (6) ispartially purified by chromatography through a short silica column (oralternatively by. Using preparative TLC on silica) using a combinationof dichloromethane-methanol-isopropylamine (typically 95:5:0.1), andthen purified by HPLC (normal-phase using silica withdichloromethane-methanol-isopropylamine or reversed phase, C-18 with0.1% TFA with acetonitrile or methanol).

Chiral resolution may be accomplished using methods such as thosedescribed in Example 22, infra.

III. INORGANIC ION RECEPTORS, DERIVATIVES, AND FRAGMENTS

The invention also relates to a superfamily of inorganic ion receptorproteins including derivatives thereof, and inorganic ion receptorfragments. Members of the superfamily related to each other bysimilarity of amino acid sequence and structure. Receptor proteins, suchas the calcium receptor, have intracellular domains, extracellulardomains, transmembrane domains, and multiple-transmembrane domains.Preferably, the novel superfamily of inorganic ion receptors have anamino acid sequence similarity of at least 15% to the human calciumreceptor (SEQ. ID. NOs. 6 and 7) and respond to inorganic ions.

Calcium receptors appear to be functionally related to a class ofreceptors which utilize so-called "G" proteins to couple ligand bindingto intracellular signals. Such "G-coupled" receptors may elicitincreases in intracellular cyclic AMP due to the stimulation of adenylylcyclase by a receptor activated "G_(S) " protein, or else may elicit adecrease in cyclic AMP due to inhibition of adenylyl cyclase by areceptor activated "G_(i) " protein. Other receptor activated G proteinselicit changes in inositol triphosphate levels resulting in release ofCa²⁺ from intracellular stores. This latter mechanism is particularlypertinent to calcium receptors.

A. Inorganic Ion Receptors

Inorganic ion receptors have an amino acid sequence encoding afunctioning inorganic ion receptor inorganic ion receptors includeproteins having the amino acid sequence of the receptor protein normallyfound in a cell and derivatives thereof. Inorganic ion receptors aredistinguished by their ability to detect and respond to changes in thelevels of inorganic ions by evoking a change in cellular function.Changes in cellular function may involve changes in secondary messengerlevels such those mediated by G protein coupled to the receptor orchanges in ionic transmembrane ion flux. Inorganic ions include cationssuch as calcium, magnesium, potassium, sodium, or hydrogen ions andanions such as phosphate or chloride ions. Ca²⁺ sensing receptors aredescribed by Herbert in U.S. application entitled. "Cloned HumanCadmium(II)-Sensing Receptor and Uses thereof," hereby incorperated byreference herein.

Regardless of the nature of the physiological ligand or activator of aninorganic ion receptor, inorganic ion receptors can be "promiscuous", inthat they can be activated by non-physiological stimuli. Thesenon-physiological stimuli may be useful, for example, to identifyanother inorganic ion receptor or to facilitate the isolation of thegene encoding it. An example of an inorganic ion receptor responding toa non-physiological stimuli is the ability of osteoclast calciumreceptor to respond not only to Ca²⁺, but also to Mn²⁺, Co²⁺ and Ni²⁺.The cations Mn²⁺ and Co²⁺ also serve to distinguish the osteoclastcalcium receptor from the parathyroid calcium receptor.

Another example of an inorganic ion receptor responding to anon-physiological stimuli is the ability of the parathyroid calciumreceptor to respond to low concentrations of La⁺ and Gd³⁺ which arehighly unlikely to be encountered under normal circumstances.Nevertheless, Gd³⁺ has been used successfully as an activator for thecalcium receptor and facilitated the cloning of this receptor byexpression in Xenopus oocytes (see Example 25).

Additionally, receptors belonging to the superfamily of inorganic ionreceptors may also be activated by stimuli other than ligand binding.For example, some members are activated by physical forces such asstretch forces acting on membranes of cells expressing inorganic ionreceptors.

B. Inorganic Ion Receptor Derivatives

Derivatives of a particular receptor have similar amino acid sequenceand retain, to some extent, one or more activities of the relatedreceptor. Derivatives have at least 15% sequence similarity, preferably70%, more preferably 90%, even more preferably 95% sequence similarityto the related receptor. "Sequence similarity" refers to "homology"observed between amino acid sequences in two different polypeptides,irrespective of polypeptide origin. The ability of the derivative toretain some activity can be measured using techniques described herein,for example, those described in Section I supra. Derivatives includemodification occurring during or after translation, for example, byphosphorylation, glycosylation, crosslinking, acylation, proteolyticcleavage, linkage to an antibody molecule, membrane molecule or otherligand (see Ferguson et al., 1988, Annu. Rev. Biochem. 57:285-320).

Specific types of derivatives also include amino acid alterations suchas deletions, substitutions, additions, and amino acid modifications. A"deletion" refers to the absence of one or more amino acid residue(s) inthe related polypeptide. An "addition" refers to the presence of one ormore amino acid residue(s) in the related polypeptide. Additions anddeletions to a polypeptide may be at the amino terminus, thecarboxyterminus, and/or internal. Amino acid "modification" refers tothe alteration of a naturally occurring amino acid to produce anon-naturally occurring amino acid. A "substitution" refers to thereplacement of one or more amino acid residue(s) by another amino acidresidue(s) in the polypeptide. Derivatives can contain differentcombinations of alterations including more than one alteration anddifferent types of alterations.

While the effect of an amino acid change varies depending upon factorssuch as phosphorylation, glycosylation, intra-chain linkages, tertiarystructure, and the role of the amino acid in the active site or apossible allosteric site, it is generally preferred that the substitutedamino acid is from the same group as the amino acid being replaced. Tosome extent the following groups contain amino acids which areinterchangeable: the basic amino acids lysine, arginine, and histidine;the acidic amino acids aspartic and glutamic acids; the neutral polaramino acids serine, threonine, cysteine, glutamine, asparagine and, to alesser extent, methionine; the nonpolar aliphatic amino acids glycine,alanine, valine, isoleucine, and leucine (however, because of size,glycine and alanine are more closely related and valine, isoleucine andleucine are more closely related); and the aromatic amino acidsphenylalanine, tryptophan, and tyrosine. In addition, althoughclassified in different categories, alanine, glycine, and serine seem tobe interchangeable to some extent, and cysteine additionally fits intothis group, or may be classified with the polar neutral amino acids.

While proline is a nonpolar neutral amino acid, its replacementrepresents difficulties because of its effects on conformation. Thus,substitutions by or for proline are not preferred, except when the sameor similar conformational results can be obtained. The conformationconferring properties of proline residues may be obtained if one or moreof these is substituted by hydroxyproline (Hyp).

Examples of modified amino acids include the following: altered neutralnonpolar amino acids such as ω-amino acids of the formula H₂ N(CH₂)_(n)COOH where n is 2-6, sarcosine (Sar), t-butylalanine (t-BuAla),t-butylglycine (t-BuGly), N-methyl isoleucine (N-MeIle), and norleucine(Nleu); altered neutral aromatic amino acids such as phenylglycine;altered polar, but neutral amino acids such as citrulline (Cit) andmethionine sulfoxide (MSO); altered neutral and nonpolar amino acidssuch as cyclohexyl alanine (Cha); altered acidic amino acids such ascysteic acid (Cya); and altered basic amino acids such as ornithine(Orn).

Preferred derivatives have one or more amino acid alteration(s) which donot significantly affect the receptor activity of the related receptorprotein. In regions of the calcium receptor protein not necessary forreceptor activity amino acids may be deleted, added or substituted withless risk of affecting activity. In regions required for receptoractivity, amino acid alterations are less preferred as there is agreater risk of affecting receptor activity. Such alterations should beconservative alterations. For example, one or more amino acid residueswithin the sequence can be substituted by another amino acid of asimilar polarity which acts as a functional equivalent.

Conserved regions tend to be more important for protein activity thannon-conserved regions. Standard procedures can be used to determine theconserved and non-conserved regions important of receptor activity usingin vitro mutagenesis techniques or deletion analyses and measuringreceptor activity as described by the present disclosure.

Derivatives can be produced using standard chemical techniques andrecombinant nucleic acid techniques. Modifications to a specificpolypeptide may be deliberate, as through site-directed mutagenesis andamino acid substitution during solid-phase synthesis, or may beaccidental such as through mutations in hosts which produce thepolypeptide. Polypeptides including derivatives can be obtained usingstandard techniques such as those described in Section I.G.2. supra, andby Sambrook et al., Molecular Cloning, Cold Spring Harbor LaboratoryPress (1989). For example, Chapter 15 of Sambrook describes proceduresfor site-directed mutagenesis of cloned DNA.

C. Receptor Fragments

Receptor fragments are portions of inorganic ion receptors. Receptorfragments preferably bind to one or more binding agents which bind to afull-length receptor. Binding agents include ionomimetics, ionolytics,and antibodies which bind to the receptor. Fragments have different usessuch as to select other molecules able to bind to a receptor.

Fragments can be generated using standard techniques such as expressionof cloned partial sequences of receptor DNA and proteolytic cleavage ofa receptor protein. Proteins are specifically cleaved by proteolyticenzymes, such as trypsin, chymotrypsin or pepsin. Each of these enzymesis specific for the type of peptide bond it attacks. Trypsin catalyzesthe hydrolysis of peptide bonds whose carbonyl group is from a basicamino acid, usually arginine or lysine. Pepsin and chymotrypsin catalyzethe hydrolysis of peptide bonds from aromatic amino acids, particularlytryptophan, tyrosine and phenylalanine.

Alternate sets of cleaved protein fragments are generated by preventingcleavage at a site which is susceptible to a proteolytic enzyme. Forexample, reaction of the ε-amino group of lysine withethyltrifluorothioacetate in mildly basic solution yields a blockedamino acid residue whose adjacent peptide bond is no longer susceptibleto hydrolysis by trypsin. Goldberger et al., Biochemistry:1:401 (1962).Treatment of such a polypeptide with trypsin thus cleaves only at thearginyl residues.

Polypeptides also can be modified to create peptide linkages that aresusceptible to proteolytic enzyme-catalyzed hydrolysis. For example,alkylation of cysteine residues with β-haloethylamines yields peptidelinkages that are hydrolyzed by trypsin. Lindley, Nature, 178:647(1956).

In addition, chemical reagents that cleave polypeptide chains atspecific residues can be used. Witcop, Adv. Protein Chem. 16:221 (1961).For example, cyanogen bromide cleaves polypeptides at methionineresidues. Gross & Witkip, J. Am. Chem. Soc. 83:1510 (1961).

Thus, by treating an inorganic ion receptor, such as, for example, ahuman calcium receptor or fragments thereof, with various combinationsof modifiers, proteolytic enzymes and/or chemical reagents, numerousdiscrete overlapping peptides of varying sizes are generated. Thesepeptide fragments can be isolated and purified from such digests bychromatographic methods. Alternatively, fragments can be synthesizedusing an appropriate solid-state synthetic procedure.

Fragments may be selected to have desirable biological activities. Forexample, a fragment may include just a ligand binding site. Suchfragments are readily identified by those of ordinary skill in the artusing routine methods to detect specific binding to the fragment. Forexample, in the case of a calcium receptor, nucleic acid encoding areceptor fragment can be expressed to produce the polypeptide fragmentwhich is then contacted with a receptor ligand under appropriateassociation conditions to determine whether the ligand binds to thefragment. Such fragments are useful in screening assays for agonists andantagonists of calcium, and for therapeutic effects where it is usefulto remove calcium from serum, or other bodily tissues.

Other useful fragments include those having only the external portion,membrane-spanning portion, or intracellular portion of the receptor.These portions are readily identified by comparison of the amino acidsequence of the receptor with those of known receptors, or by otherstandard methodology. These fragments are useful for forming chimericreceptors with fragments of other receptors to create a receptor with anintracellular portion which performs a desired function within thatcell, and an extracellular portion which causes that cell to respond tothe presence of ions, or those agonists or antagonists described herein.Chimeric receptor genes when appropriately formulated are useful ingenetic therapies for a variety of diseases involving dysfunction ofreceptors or where modulation of receptor function provides a desirableeffect in the patient.

Additionally, chimeric receptors can be constructed such that theintracellular domain is coupled to a desired enzymatic process which canbe readily detected by calorimetric, radiometric, luminometric,spectrophotometric or fluorimetric assays and is activated byinteraction of the extracellular portion with its native ligand (e.g.,calcium) or agonist and/or antagonists of the invention. Cellsexpressing such chimeric receptors can be used to facilitate screeningof inorganic ion receptor agonists and antagonists.

IV. Nucleic Acids Encoding Ion-Receptors

The invention also features nucleotide sequences encoding inorganic ionreceptors and receptor fragments. Nucleotide sequences encodinginorganic ion receptors may be obtained from organisms through a varietyof procedures, such as through the use of hybridization probes,antibodies binding a receptor, gene walking, and/or expression assays.

A nucleic acid encoding a particular receptor provides for additionaltools to obtain more receptors, for example by providing forhybridization assay probes and antibodies. Furthermore, sequenceinformation from two or more receptors can be analyzed to determinelocalized sequence conservation which is useful for obtaining stilladditional clones encoding other members of the superfamily. Conservedsequences also may be derived from an analysis of the overall structureof BoPCaR 1, as it conventionally includes an extracellular domain,transmembrane domain and intracellular domain.

"Conserved nucleic acid regions" refers to two or more nucleic acidsencoding an inorganic ion receptor, preferably a calcium receptor, towhich a particular nucleic acid sequence can hybridize to under lowerstringency conditions. Examples of lower stringency conditions suitablefor screening for nucleic acid encoding inorganic ion receptors areprovided in the examples below and in Abe et al. J. Biol. Chem.,19:13361 (1992) (hereby incorporated by reference herein). Preferably,conserved regions differ by no more than 7 out of 20 nucleotides.

In preferred embodiments the purified nucleic acid encodes anextracellular domain, but is substantially free of transmembrane andintracellular domains; the purified nucleic acid encodes anintracellular domain, but is substantially free of transmembrane andextracellular domains; the purified nucleic acid encodes a transmembranedomain, but is substantially free of an extracellular or intracellulardomain; the purified nucleic acid encodes a multiple-transmembranedomain (e.g., a seven-transmembrane domain), but is substantially freeof C-terminal intracellular and N-terminal extracellular regions; thepurified nucleic acid encodes an extracellular domain which istranscriptionally coupled to nucleic acid encoding a transmembrane,multiple-transmembrane, and/or intracellular domain of a non-inorganicion receptor or a different inorganic ion receptor and results in afusion protein; the purified nucleic acid encodes an extracellulardomain of a non-inorganic ion receptor or a different inorganic ionreceptor which is transcriptionally coupled to nucleic acid encoding atransmembrane, multiple-transmembrane, and/or intracellular domain of aninorganic ion receptor and results in a fusion protein.

In addition, isolated nucleic acid sequences of the invention may beengineered so as to modify processing or expression of receptorsequences. For example, the coding sequence may be combined with anexogenous promoter sequence and/or a ribosome binding site. Anotherexample, is that codons may be modified such that while they encode anidentical amino acid, that codon may be a preferred codon in the chosenexpression system.

Additionally, a given coding sequence can be mutated in vitro or invivo, to create variations in coding regions and/or form new restrictionendonuclease sites or destroy preexisting ones, to facilitate further invitro modification. Standard recombinant techniques for mutagenesis suchas in vitro site-directed mutagenesis (Hutchinson et al., J. Biol. Chem.253:6551, (1978), Sambrook et al., chapter 15, supra), use of TAB®linkers (Pharmacia), and PCR-directed mutagenesis can be used to createsuch mutations.

Cloning the calcium receptor from different cells will allow thepresence of homologous proteins in other cells to be directly assessed.A family of structurally homologous calcium receptor proteins can thusbe obtained. Such receptors will allow understanding of how these cellsdetect extracellular Ca²⁺ and enable evaluation of the mechanism(s) as asite of action for the therapeutics described herein effective in thetreatment of for example, HPT, osteoporosis, and hypertension, and noveltherapies for other bone and mineral-related diseases.

A. Assays To Detect Receptors

Various assays can be used to detect the presence of an inorganic ionreceptor such as calcium receptor and fragments thereof. Such assaysinclude detecting the presence of receptor protein, or receptoractivity, expressed by nucleic acid encoding the receptor. Examples ofassays for measuring calcium receptor activity are described below.Equivalent assays for other inorganic ion receptors such as Na⁺, K⁺, andphosphate are known in the art.

1. Measurement of Receptor Activity

The ability of nucleic acid to encode a functioning calcium receptor canbe conveniently measured using a Xenopus expression assay to detectincreases in intracellular Ca²⁺ due to receptor activation. Increases inintracellular Ca²⁺ can be measured by different techniques such as bymeasuring current through the endogenous Ca²⁺ -activated Cl⁻ channel;loading oocytes with ⁴⁵ Ca²⁺ and measuring mobilization of ⁴⁵ Ca²⁺ fromintracellular stores; and using fluorescent Ca²⁺ indicators. Expressionassays can also be used to measure the calcimimetic and calcilyticactivity of agents using Xenopus egg containing nucleic acid expressinga functioning calcium receptor.

Receptors are activated by using receptor ligands, such as neomycin,Gd³⁺, Ca²⁺, Mg²⁺ or other calcimimetic compound. The ability ofreceptors to be activated by calcimimetics can be measured in a Xenopusexpression assay. For example, molecules can be tested for their abilityto elicit increases in intracellular Ca²⁺ in Xenopus oocytes containingnucleic acid expressing a functioning calcium receptor indirectly bymeasuring current through the endogenous Ca²⁺ -activated Cl⁻ channel.The amplification of the response afforded by this signal transductionpathway enables the detection of receptor proteins encoded by mRNA atvery low levels. This allows the detection of receptor-specific cDNAclones without the need for high-affinity ligands, specific antisera, orprotein or nucleic acid sequence information.

For example, for each mRNA fraction, 10-20 oocytes are injected with 50ng of RNA at a concentration of 1 ng/nl in water. Injected oocytes aremaintained at 18° C. for 48-72 hours, after which they are assessed forexpression of the calcium receptor using measurements of Cl⁻ current.For each group of injected oocytes, the number positive for expressionof the receptor, as well as the magnitude of the Ca²⁺ -dependent Cl⁻current measured, is determined. As negative controls, oocytes areinjected with rat liver poly(A)⁺ -enriched mRNA, yeast RNA, or water.

2. Measuring the Presence of a Receptor

The presence of a receptor protein or polypeptide fragment can becarried using agents which bind to the receptor. The binding agentshould have a group which readily indicates its presence, such as aradiolabel, or group which can be easily detected, such as an antibody.

Antibodies can be used to screen expression libraries, such as cDNAlibraries in λgtll to determine the presence of clones expressingantigenically reactive protein. Screening can be carried out usingstandard techniques. Sambrook et al., Molecular Cloning, chapter 18,Cold Spring Harbor Laboratory Press (1989. Clones testing positive canbe purified and then sequenced to determine whether they encode acalcium receptor.

Similarly phage display libraries can be used to clone and analyzecalcium receptors in place of monoclonal antibodies. In these libraries,antibody-variable regions or random peptides are shotgun cloned intophage expression vectors such that the antibody regions or peptides aredisplayed on the surface of the phage particle. Phage(s) which displayantibody regions or peptides capable of high specific binding to calciumreceptors will bind to cells which display these receptors (e.g.,parathyroid cells, C-cells, osteoclasts, etc.). Hundreds of millions ofsuch phage can be panned against these cell types preferentiallyselecting those phage which can bind to these cells (which includesthose phage binding to calcium receptors). In this manner, thecomplexity of the library can be vastly reduced. Iterative repetition ofthis process results in a pool of phage which bind to the cell typeused. Subsequently, screens for monoclonal antibodies can be used toisolate phage displaying a calcium receptor-binding antibody or peptideregions, and these phage can be used to isolate the calcium receptor forpurposes of structural identification and cloning. Kits to prepare suchphage-display libraries are commercially available (e.g., Stratacyte, orCambridge Antibody Technology Limited).

Recombinant phage endowed with such calcium receptor-binding propertiescan also be used in lieu of monoclonal antibodies in the variousanalyses of calcium receptors. Such phage can also be used inhigh-throughput binding-competition screens to identify organiccompounds capable of functional binding to calcium receptors which canserve as structural leads for the development of human therapeuticsacting at the calcium receptor.

In another alternative, affinity cross-linking of radioligands to theirreceptors can be used to isolate the receptor protein as described byPilch & Czech, 1 Receptor Biochem. Methodol. 161, 1984. Covalentattachment of a radioligand allows extensive washing to removenon-specific binding. For example, a high-affinity molecule, e.g., arandom copolymer of arginine and tyrosine (MW=22K; argtyr ratio=4:1)which mobilizes intracellular Ca²⁺ with an EC₅₀ of about 100 nM or less,is iodinated with ¹²⁵ I, and cross-linked. Protamines, because of theirmuch smaller size, may be preferable in cross-linking studies and can bereductively alkylated as described by Dottavio-Martin & Ravel, 87Analyt. Biochem. 562, 1978.

Nonspecific labelling is kept to a minimum by cross-linking in thepresence of unlabeled polycations and di- and trivalent cations. At highconcentrations of these molecules, nonspecific interactions of the labelwith the cell surface might be reduced.

B. Expression Assay

This section describes techniques to clone bovine and human parathyroidcell calcium receptor cDNAs by functional expression in Xenopus oocytes.Adult female Xenopus laevis were obtained from Xenopus I (Ann Arbor,Mich.) and maintained according to standard procedures. Lobes of ovarywere excised from hypothermically anesthetized toads. Clusters ofoocytes were transferred into modified Barth's saline (MBS). Individualoocytes were obtained by incubation in MBS containing 2 mg/mlcollagenase (Sigma, Type 1A) for 2 hours at 21° C. and stage V-VIoocytes were selected for injection.

Glass capillary tubes (1 mm diameter) were pulled to a fine tip andmanually broken to achieve a tip diameter of about 15 μmeters. A dropletof mRNA (1 ng/nl in diethylpyrocarbonate (DEPC)-treated water) wasplaced onto PARAFILM™ and drawn into the capillary tube by suction. Thecapillary tube was then connected to a picospritzer (WPI Instruments)and the volume of the air-pulsed droplets adjusted to deliver 50 ng ofmRNA (typically 50 nl). A 35-mm culture dish with a patch of nylonstocking fixed to the bottom was used to secure the oocytes duringinjection of mRNA into the vegetal pole. The injected oocytes wereplaced into a 35-mm culture dish containing MBS, 100 μg/ml penicillinand 100 μg/ml streptomycin and incubated at 18° C. for 3 days.

Following incubation, an oocyte was placed into a 100-μl plastic chamberand superfused with MBS at a flow rate of 0.5 ml/min using a peristalticpump. Test molecules or inorganic polycations were added by rapidlymoving the tubing into different buffers. Recording and current passingelectrodes were constructed from thin-wall capillary tubing pulled to aresistance of 1-3 Mohms and filled with 3M KCl. Oocytes were impaled (inthe animal pole) with both electrodes under microscopic observation andconnected to an Axon Instruments Axoclamp 2A voltage-clamp amplifierwhich was used to set the holding potential (-70 to -80 mV) and tomeasure the currents that were passed to maintain the holding potential.Currents were recorded directly onto a strip chart recorder.

For mRNA preparation, tissue was obtained from calves or patients withsecondary HPT undergoing surgical removal of the parathyroid glands.Whole pieces of gland were used to prepare mRNA that directs theexpression of the calcium receptor in Xenopus oocytes. Total cellularRNA was obtained by acid guanidinium thiocyanate/phenol extraction ofhomogenized glands. Oligo-dT cellulose chromatography was used to selectpoly(A)⁺ -mRNA by standard procedures.

Size fractionation of mRNA was carried out by centrifugation throughglycerol gradients. The mRNA was denatured with 20 mM methylmercurichydroxide and loaded (50-100 μg at a concentration of 1 mg/ml) onto alinear 15-30% glycerol gradient prepared in Beckman TLS55 tubes.Following centrifugation at 34,000 rpm for 16 hours, 0.3 ml gradientfractions were collected and diluted in an equal volume of watercontaining 5 mM beta-mercaptoethanol. The mRNA was then recovered by twocycles of ethanol precipitation.

The mRNA (50-100 μg of poly(A)⁺) can also be separated on a 1.2%agarose/6.0M urea preparative gel, along with a range of RNA sizemarkers. Following visualization of the mRNA by ethidium bromidestaining, gel slices containing RNA approximately 1 kb to 2 kb in sizeare excised. The mRNA is recovered from the agarose gel slices usingRNAid binding matrix (according to the supplier's standard protocol;Stratagene, Inc.) and recovered mRNA fractions eluted into DEPC-treatedwater.

Amounts of recovered mRNA were quantified by UV absorbance measurement.The size range of mRNA contained within each fraction of the glycerolgradient was determined by formaldehyde/agarose gel electrophoresisusing a small quantity (0.5 μg) of each sample.

The integrity of the mRNA was assessed by in vitro translation.Reticulocyte lysates (commercially available kits; BRL) were used totranslate 0.05-0.5 μg of each mRNA fraction. The resulting ³⁵ S-labelledproteins were analyzed by SDS-PAGE. Intact mRNA was capable of directingthe synthesis of proteins of a complete size range, correspondingroughly to the sizes of the individual mRNA fractions.

A cDNA library was then constructed in the vector λ ZAPII, using amodifications of the techniques described by Gubler and Hoffman. RNAfractions were tested for their ability to induce Cl⁻ current. Fractionsgiving the best response in the oocyte assay were used as startingmaterial for cDNA synthesis.

First-strand cDNA synthesis was primed with an oligo-dT/NotIprimer-linker. Second-strand synthesis was performed using the RNaseH/DNA Polymerase I self-priming method. Double-stranded cDNA was bluntedwith T4 DNA polymerase and EcoRI adaptors blunt-end ligated to the cDNAwith T4 ligase. Following NotI digestion to cleave the linker,full-length cDNA was size-selected by exclusion chromatography onSephacryl 500 HA. First-strand cDNA was radiolabeled with α-³² P-dATP,and all synthesis and recovery steps monitored by following theincorporation of radioactivity. Full-length cDNA recovered from thesizing column was ligated to EcoRI/NotI digested λ ZAPII arms. Theligation mix was test packaged with commercially availablehigh-efficiency packaging extract (Stratagene, Inc.) and plated on theappropriate host strain (XL1-blue). The percentage of recombinant phagewas determined by the ratio of white-to-blue plaques when the librarywas plated on IPTG and X-gal.

The average insert size was determined from ten randomly selectedclones. Phage DNA "mini-preps" were digested with EcoRI and NotI torelease the insert, and the size determined by agarose gelelectrophoresis. The library consisted of >90% recombinant phage, andthe insert size ranged from 1.5 to 4.2 kb. The recombinant ligation waspackaged in large scale to generate 800,000 primary clones. Thepackaging mix was titered and plated at 50,000 plaques per 15 cm plate.Each pool of 50,000 clones was eluted in SM buffer and storedindividually.

Plate lysate stocks of each of the clone pools were used for small-scalephage DNA preparation. Phage particles were concentrated by polyethyleneglycol precipitation, and phage DNA purified by proteinase K digestionfollowed by phenol-chloroform extraction. Twenty micrograms of DNA weredigested with NotI, and used as template for in vitro transcription ofsense-strand RNA. In vitro transcription was carried out according tostandard protocols, utilizing T7 RNA polymerase and 5' cap analog m⁷GpppG in a 50 μl total reaction volume. Following Dnase I/Proteinase Kdigestion and phenol-chloroform extraction, the RNA was concentrated byethanol precipitation and used for oocyte injection.

Oocytes were injected with synthetic mRNA (cRNA) from each of the 16library subpools constituting 50,000 independent clones each. Afterincubation for 3 to 4 days, oocytes were assayed for the ability of 10mM neomycin to elicit a Ca²⁺ -dependent Cl⁻ current. A pool designated"pool 6" gave a positive signal and thus contains a cDNA clone encodinga functional calcium receptor.

Pool 6 phage was replated at about 20,000 plaques per plate and 12plates harvested. DNA was prepared from each of these subpools and cRNAsynthesized. Again, oocytes were injected with cRNA and assayed 3-4 dayslater for the ability of 10 mM neomycin to elicit a Ca²⁺ -dependent Cl⁻current. A subpool, pool 6-3, was positive and this pool was subjectedto a further round of plating, reducing the complexity of pools toaround 5,000 clones per pool. Pools were again assayed by preparation ofcRNA and injection in oocytes. A subpool, pool 6-3.4, was positive.

To further purify the positive clone in pool 6-3.4, phage DNA from thispool was rescued as plasmid DNA by superinfection with the helper phage,ExAssist (Stratagene). Transfection of rescued plasmids into bacterialstrain DH5alphaF' resulted in transformed bacterial colonies onampicillin plates. These were harvested in pool of 900 clones each.Plasmid DNA was then prepared from each subpool and cRNA synthesized andassayed in the usual manner. Subpool 6-3.4.4 was positive.

Bacteria containing the plasmid subpool 6-3.4.4 were subsequently platedin subpools of about 50 clones each. Continuation of this process isexpected to resulted in a single clone encoding a functional calciumreceptor.

3. Calcium-Trapping Assay

This section describes a "calcium-trapping assay" for the detection ofCOS 7 cells expressing G protein-coupled receptors. In this assay COS 7cell monolayers are transfected with cDNA clones from a bovineparathyroid cDNA library (e.g., subfractions or pools from a libraryprepared in pCDNA1) and are assayed for their ability to trapradioactive ⁴⁵ Ca²⁺ in response to treatment with an agonist for thecalcium receptor. The monolayers undergo emulsion autoradiography andcells that have trapped ⁴⁵ Ca²⁺ are identified by the presence ofphotographic grain clusters under dark-field microscopy. Library poolsthat produce a positive signal are then sequentially subdivided until asingle cDNA that produces the signal is identified.

C. Hybrid-Depletion Assay

A hybrid depletion assay can be used to obtain mRNA encoding inorganicion receptors. In this approach, clones are selected on the basis oftheir ability to deplete a specific mRNA species from the total mRNApopulation. A clone encoding a single subunit is identified by itsability to prevent the formation of the active multi-subunit complex. Byexhaustive screening it is possible to identify clones encoding all ofthe necessary subunits.

Thus, the hybrid-depletion screening strategy can result in theisolation of clones that do not contain a complete protein codingregion. Positive clones isolated by this screening strategy aresequenced to determine their protein coding capacity. Northern blotanalysis of human parathyroid gland RNA permits the determination of thesize of the complete mRNA corresponding to specific clones. If positiveclones do not appear to be full length, the cloned cDNA will be used asa hybridization probe to screen a parathyroid gland cDNA library forcomplete cDNAs.

For example, human parathyroid cells express a beta-adrenergic receptorcoupled to adenylate cyclase. This receptor can be expressed in oocytes,where it is capable of agonist-induced activation of the endogenousadenylate cyclase. During the hybrid-depletion screening for Ca²⁺receptor clones, oocytes injected with hybrid-depleted mRNA are assayedfor isoproterenol-induced adenylate cyclase activation. A positiveresponse in this assay serves to indicate that any observed inhibitionof Ca²⁺ receptor response is specific, and not due to a generalinhibition of G protein receptor functions.

D. Cloning Using Hybridization Probes and Primers

The presently preferred method for isolating inorganic ion receptornucleic acid is based upon hybridization screening. Region-specificprimers or probes derived from nucleic acid encoding a calcium receptorcan be used to prime DNA synthesis and PCR amplification, as well as toidentify colonies containing cloned DNA encoding a member of theinorganic ion receptor family using known methods (e.g., Innis et al.,PCR Protocols, Academic Press, San Diego, Calif. (1990)).

1. PCR Cloning

Primer hybridization specificity to target nucleic acid encoding aninorganic ion receptor can be adjusted by varying the hybridizationconditions. When annealing at higher stringency conditions of 50°-60°C., sequences which are greater than about 76% homologous to the primerwill be amplified. By employing lower stringency conditions, annealingat 35°-37° C., sequences which are greater than about 40-50% homologousto the primer will be amplified.

Analysis of the calcium receptor indicates that it is a Gprotein-coupled receptor having seven conserved. One particularly usefulapproach is to employ degenerate primers homologous to the conservedtransmembrane domain coding regions and to amplify DNA regions encodingthese sequences using polymerase chain reaction (PCR). Thus, sucholigonucleotide primers are mixed with genomic DNA or cDNA to RNAisolated from the tissue of choice and PCR carried out. Someexperimentation may be required to specifically amplify novel Gprotein-coupled receptor sequences from the tissue of choice since theseare not necessarily identical to already known G protein-coupledreceptors, but this is well understood by those of ordinary skill in theart (see, for example, Buck, L. and Axel, R. (1991) Cell, 65:175-187).

2. Hybridization Assay Probes

Hybridization assay probes can be designed based on sequence informationobtained from cloned calcium receptors and amino acid sequences encodingsuch receptors. Hybridization assay probes can be designed to detect thepresence of a particular nucleic acid target sequence perfectlycomplementary to the probe and target Sequences of lessercomplementarity by varying the hybridization conditions and probedesign.

DNA probes targeted to inorganic ion receptors can be designed and usedunder different hybridization conditions to control the degree ofspecificity needed for hybridization to a target sequence. Factorsaffecting probe design, such as length, G and C content, possibleself-complementarity, and wash conditions, are known in the art. (See,for example, Sambrook et al., Molecular Cloning, Cold Spring HarborLaboratory Press (1989).) Sambrook et al., Molecular Cloning, alsodiscusses the design and use of degenerative probes based on sequencepolypeptide information.

As a general guideline, high stringency conditions (hybridization at50°-65° C., 5X SSPC, 50% formamide, wash at 50°-65° C., 0.5X SSPC) canbe used to obtain hybridization between nucleic acid sequences havingregions which are greater than about 90% complementary. Low stringencyconditions (hybridization at 35°-37° C., 5X SSPC, 40-45% formamide, washat 42° C. SSPC) can be used so that sequences having regions which aregreater than 35-45% complementarity will hybridize to the probe.

Any tissue encoding an inorganic ion receptor can be used as a sourcefor genomic DNA. However, with respect to RNA, the most preferred sourceis tissues which express elevated levels of the desired inorganic ionreceptor family member.

E. Targeting Gene Walking

Targeted gene walking (TGW) is a modification of a standard polymerasechain reaction (PCR) that allows amplification of unknown DNA sequencesadjacent to short segments of known sequence. Parker et al., Nucl. AcidsRes., 19: 3055 (1991). Unlike conventional PCR techniques that amplifyDNA sequences between two known primer sites, TGW can amplify DNAadjacent to one such site. Thus, TGW can serve as a replacement forconventional cloning and library screening methods for isolatingsequences upstream or downstream from known sequences. The procedure canbe used to isolate genes from any starting DNA template for which alimited amount of sequence information is known.

For example, first, several standard PCR reactions are run in parallelusing one "targeted primer" and different "walking primers." Thetargeted primer is a sequence-specific primer exactly complementary to aknown sequence on the DNA molecule of interest, and is directed towardsunknown adjacent sequences. The walking primers are non-specificsequences not complementary to DNA near the target primer. The walkingprimers can be any oligonucleotides unrelated to the target primersequence.

In the first series of PCR, products are produced only when a walkingprimer anneals to a DNA strand contiguous with and complementary to thestrand to which the targeted primer has hybridized. The PCR products ofinterest are preferably within the 5 kilobase size range. Amplificationproducts are produced with as many as 60% mismatched nucleotides withinthe walking primer relative to DNA template. Perfect base-pairing isrequired only for the first two 3' nucleotides of the walking primer,but partial homology is tolerated otherwise. Annealing temperature is akey variable in determining the number of PCR products, as identified byagarose gel electrophoresis.

Second, an oligomer extension assay is performed using an "internaldetection primer." This primer represents known sequences between theprevious two primers, contiguous with the targeted primer. The internaldetection primer is kinased with ³² P-gamma-ATP, then used in a singlePCR cycle with DNA from the first PCR as template. This extensionidentifies products in the first PCR contiguous with the targetedprimer. These new products are identified by agarose gel electrophoresisand autoradiography. Any products that do not hybridize to the internaldetection primer represent non-contiguous amplification productsproduced by any subset of the primers.

Last, bands identified in the oligomer extension assay are excised fromthe gel, and reamplified by standard PCR using target primer and thewalking primer that produced the band initially. This new PCR band isthen sequenced directly to provide previously unknown sequenceinformation.

To extend information in the opposite direction, complements are made ofthe targeted and internal detection primers, and their order is reversedin the protocol. The pieces of information obtained from going in bothdirections are combined.

V. Antibodies

Inorganic ion receptors, derivatives, and fragments thereof retainingantigenic determinants can be used to generate antibodies recognizing aninorganic ion receptor. Both polyclonal and monclonal antibodies can begenerated. Because derivatives have a different amino acid sequence thanthe inorganic ion receptor, the derivative may not have all theantigenic determinants of the inorganic ion receptor which it is relatedto and may have some different antigenic determinants. Preferably, theinorganic ion receptor is a calcium receptor.

Antibodies can be produced and used to purify proteins using standardtechniques such as those described by Harlow and Lane in Antibodies, aLaboratory Manual, Cold Spring Harbor Laboratory, 1988. Sources ofimmunogens for antibody production include purified inorganic ionreceptors, purified inorganic ion receptor fragments, and whole cellsexpressing an inorganic ion receptor. Preferably, the immunogen is apurified calcium receptor, purified calcium receptor fragment, or wholecells expressing a purified calcium receptor. An example for obtainingantibodies to a calcium receptor from bovine parathyroid is describedbelow.

For example, whole bovine parathyroid gland cells as the immunogen.Purified, dispersed cells are obtained, and live or fixed cellpreparations are injected intraperitoneally into the appropriate mousestrain, according to established procedures. Standard protocols arefollowed for immunization schedules and for the production ofhybridomas. A two-step screening procedure is used to identifyhybridomas secreting monoclonal antibodies that recognize the calciumreceptor.

The initial screen identifies monoclonal antibodies recognizingparathyroid cell surface antigens. Immunohistochemical techniques arethen used to screen hybridoma supernatants for the presence of mouseantibodies that bind to the surface of parathyroid cells. The secondscreen can be performed on fixed sections of parathyroid gland tissue,or on dispersed cells in primary culture.

This procedure identifies hybridomas producing monoclonal antibodies toa variety of cell-surface determinants, and monoclonals specific for thecalcium receptor would be expected to comprise only a small subset ofthese. To identify monoclonal antibodies that bind to the calciumreceptor, hybridoma supernatants that test positive in the initialscreen are assayed for their ability to block the response of culturedparathyroid cells to calcium receptor agonists. Some antibodies thatbind to the extracellular domain of the receptor are expected to inhibitor activate ligand binding or to otherwise interfere with or affectreceptor activation.

Monoclonal antibodies positive in both screens are characterized throughwestern blotting, immunoprecipitation and immunohistochemistry. Thispermits the determination of the size of the antigen that is recognizedand its tissue distribution. The appropriate monoclonal antibody is thenused for purification of the calcium receptor protein by immunoaffinitychromatography, following standard techniques.

Polyclonal antibodies recognizing an ion receptor may be obtained byimmunizing rabbits or other mammals with isolated ion receptorpolypeptides. Polypeptides used for immunization can comprise the entirereceptor polypeptide or fragments thereof.

Ion receptor polypeptides may be isolated from tissues or cells normallyexpressing the ion receptor of choice, or from cells constructed for thepurpose of recombinant expression of such polypeptides.

VI. Highlighted Uses

This section highlights and expands on some of the uses of theionomimetic and/or ionolytic molecules, receptor polypeptides, nucleicacids encoding receptor polypeptides and antibodies recognizing receptorpolypeptides. Additional uses are discussed in other parts of theapplication and are apparent to one of ordinary skill in the art readingthe application.

A. Treatment of Diseases

Diseases or disorders which can be treated by modulating calciumreceptor activity are known in the art. For example, diseases ordisorders which can be treated by modulating calcium receptor activitycan be identified based on the functional responses of cells regulatedby calcium receptor activity. Functional responses of cells regulated bycalcium receptor are know in the art, including PTH secretion byparathyroid cells, calcitonin secretion by C-cells, and bone resorptionby osteoclasts.

Such functional responses are associated with different diseases ordisorders. For example, hyperparathyroidism results in elevated levelsof PTH in the plasma. Decreasing the plasma levels of PTH offers aneffective means of treating hyperparathyroidism. Likewise, increasingplasma levels of calcitonin is associated with an inhibition of boneresorption. Inhibiting bone resorption is an effective treatment forosteoporosis. Thus, modulation of calcium receptor activity can be usedto treat diseases such as hyperparathyroidism, and osteoporosis.

Those compounds modulating inorganic ion receptor activity, preferablycalcium receptor activity, can be used to confer beneficial effects topatients suffering from a variety of diseases or disorders. For example,osteoporosis is an age-related disorder characterized by loss of bonemass and increased risk of bone fracture. Compounds can be used to blockosteoclastic bone resorption either directly (e.g., an osteoclastionomimetic compound) or indirectly by increasing endogenous calcitoninlevels (e.g., a C-cell calcimimetic). Alternatively, a calcilytic activeon the parathyroid cell calcium receptor will increase circulatinglevels of parathyroid hormone, stimulating bone formation. All three ofthese approaches will result in beneficial effects to patients sufferingfrom osteoporosis.

In addition, it is known that intermittent low dosing with PTH resultsin an anabolic effect on bone mass and appropriate bone remodeling.Thus, compounds and dosing regimens evoking transient increases inparathyroid hormone (e.g., intermittent dosing with a parathyroid cellionolytic) can increase bone mass in patients suffering fromosteoporosis.

Additional diseases or disorders can be identified by identifyingadditional cellular functional responses, associated with a disease ordisorder, which are regulated by calcium receptor activity. Diseases ordisorder which can be treated by modulating other inorganic ionreceptors can be identified in an analogous manner.

Patient treatment can be carried out using different molecules describedherein including: (1) inorganic ion receptor-modulating agents,preferably calcium receptor-modulation agents; (2) inorganic ionreceptor proteins and fragments thereof, preferably calcium receptorproteins and fragments thereof; (3) nucleic acids encoding inorganic ionreceptor proteins and fragments thereof, preferably calcium receptorproteins and fragments thereof; and (4) antibodies, and fragmentsthereof targeted to inorganic ion receptor proteins, preferably acalcium receptor.

1. Inorganic Ion Receptor-Modulating Agents

The inorganic ion receptor-modulating agents of the present inventioncan exert an affect on an inorganic ion receptor causing one or morecellular effects ultimately producing a therapeutic effect. Differenttypes of diseases or disorders can be treated by modulating inorganicion receptor activity, preferably calcium receptor activity, such asthose having one or more of the following: (1) those characterized byabnormal inorganic ion homeostasis, preferably, calcium homeostasis; (2)those characterized by an abnormal amount of an extracellular orintracellular messenger whose production can be affected by inorganicion receptor activity, preferably calcium receptor activity; and (3)other diseases or disorders in which modulation of inorganic ionreceptor activity, preferably calcium receptor activity, will exert abeneficial effect, for example, in diseases or disorders ,where theproduction of an intracellular or extracellular messenger stimulated byreceptor activity compensates for an abnormal amount of a differentmessenger.

Calcium receptor-modulating agents of the present invention can exert aneffect on calcium receptor causing one or more cellular effectsultimately producing a therapeutic effect. Different diseases can betreated by the present invention by targeting cells having a calciumreceptor. For example, primary hyperparathyroidism (HPT) ischaracterized by hypercalcemia and abnormal elevated levels ofcirculating PTH. A defect associated with the major type of HPT is adiminished sensitivity of parathyroid cells to negative feedbackregulation by extracellular Ca²⁺. Thus, in tissue from patients withprimary HPT, the "set-point" for extracellular Ca²⁺ is shifted to theright so that higher than normal concentrations of extracellular Ca²⁺are required to depress PTH secretion. Moreover, in primary HPT, evenhigh concentrations of extracellular Ca²⁺ often depress PTH secretiononly partially. In secondary (uremic) HPT, a similar increase in theset-point for extracellular Ca²⁺ is observed even though the degree towhich Ca²⁺ suppresses PTH secretion is normal. The changes in PTHsecretion are paralleled by changes in Ca²⁺ !_(i) : the set-point forextracellular Ca²⁺ -induced increases in Ca²⁺ !_(i) is shifted to theright and the magnitude of such increases is reduced.

Molecules that mimic the action of extracellular Ca²⁺ are beneficial inthe long-term management of both primary and secondary HPT. Suchmolecules provide the added impetus required to suppress PTH secretionwhich the hypercalcemic condition alone cannot achieve and, thereby,help to relieve the hypercalcemic condition. Molecules with greaterefficacy than extracellular Ca²⁺ may overcome the apparentnonsuppressible component of PTH secretion which is particularlytroublesome in the major form of primary HPT caused by adenoma of theparathyroid gland. Alternatively or additionally, such molecules candepress synthesis of PTH, as prolonged hypercalcemia has been shown todepress the levels of preproPTH mRNA in bovine and human adenomatousparathyroid tissue. Prolonged hypercalcemia also depresses parathyroidcell proliferation in vitro, so calcimimetics can also be effective inlimiting the parathyroid cell hyperplasia characteristic of secondaryHPT.

Cells other than parathyroid cells can respond directly to physiologicalchanges in the concentration of extracellular Ca²⁺. For example,calcitonin secretion from parafollicular cells in the thyroid (C-cells)is regulated by changes in the concentration of extracellular Ca²⁺.

Isolated osteoclasts respond to increases in the concentration ofextracellular Ca²⁺ with corresponding increases in Ca²⁺ !_(i) that arisepartly from the mobilization of intracellular Ca²⁺. Increases in Ca²⁺!_(i) in osteoclasts are associated with the inhibition of boneresorption. Release of alkaline phosphatase from bone-formingosteoblasts is directly stimulated by calcium.

Renin secretion from juxtaglomerular cells in the kidney, like PTHsecretion, is depressed by increased concentrations of extracellularCa²⁺. Extracellular Ca²⁺ causes the mobilization of intracellular Ca²⁺in these cells. Other kidney cells respond to calcium as follows:elevated Ca²⁺ inhibits formation of 1,25(OH)₂ -vitamin D by proximaltubule cells, stimulates production of calcium-binding protein in distaltubule cells, and inhibits tubular reabsorption of Ca²⁺ and Mg²⁺ and theaction of vasopressin on the thick ascending limb of Henle's loop(MTAL), reduces vasopressin action in the cortical collecting ductcells, and affects vascular smooth muscle cells in blood vessels of therenal glomerulus.

Calcium also promotes the differentiation of intestinal goblet cells,mammary cells, and skin cells; inhibits atrial natriuretic peptidesecretion from cardiac atria; reduces cAMP accumulation in platelets;alters gastrin and glucagon secretion; acts on vascular smooth musclecells to modify cell secretion of vasoactive factors; and affects cellsof the central nervous system and peripheral nervous system.

Thus, there are sufficient indications to suggest that Ca²⁺, in additionto its ubiquitous role as an intracellular signal, also functions as anextracellular signal to regulate the responses of certain specializedcells. Molecules of this invention can be used in the treatment ofdiseases or disorders associated with disrupted Ca²⁺ responses in thesecells.

Specific diseases and disorders which might be treated or prevented,based upon the affected cells, also include those of the central nervoussystem such as seizures, stroke, head trauma, spinal cord injury,hypoxia-induced nerve cell damage such as in cardiac arrest or neonataldistress, epilepsy, neurodegenerative diseases such as Alzheimer'sdisease, Huntington's disease and Parkinson's disease, dementia, muscletension, depression, anxiety, panic disorder, obsessive-compulsivedisorder, post-traumatic stress disorder, schizophrenia, neurolepticmalignant syndrome, and Tourette's syndrome; diseases involving excesswater reabsorption by the kidney such as syndrome of inappropriate ADHsecretion (SIADH), cirrhosis, congestive heart failure, and nephrosis;hypertension; preventing and/or decreasing renal toxicity from cationicantibiotics (e.g., aminoglycoside antibiotics); gut motility disorderssuch as diarrhea, and spastic colon; GI ulcer diseases; GI diseases withexcessive calcium absorption such as sarcoidosis; and autoimmunediseases and organ transplant rejection.

While calcium receptor-modulating agents of the present invention willtypically be used in therapy for human patients, they may also be usedto treat similar or identical diseases in other warm-blooded animalspecies such as other primates, farm animals such as swine, cattle, andpoultry; and sports animals and pets such as horses, dogs and cats.

B. Toxin Binding Agents

The invention further provides receptor-binding agents includingantibodies and/or fragments thereof which can be conjugated to a toxinmoiety, or expressed along with a toxin moiety as a recombinant fusionprotein. The toxin moiety will bind to and enter a target cell using theinteraction of the binding agent and the corresponding target cellsurface receptor. The toxin moiety results in targeted cell death. Thus,cells having calcium receptors characteristic of a disease or disorder,such as cancers, can be targeted by the present invention.

Suitable toxin moieties bound to a binding agent include proteins suchas pokeweed anti-viral protein, abrin, diphtheria exotoxin, orPseudomonas exotoxin; ricin, and a high energy-emitting radionuclidesuch as cobalt-60. Other examples of possible toxin moieties are knownin the art. See, for example, "Conjugate Vaccines", Contributions toMicrobiology and Immunology, J. M. Cruse and R. E. Lewis, Jr. (eds.),Carger Press, New York, (1989). The chosen toxin moiety should bepharmaceutically acceptable.

The conjugation of the binding agent to another moiety (e.g., bacterialtoxin) can be accomplished by linking the two molecules using standardtechniques so long as both molecules retain their respective activity.Possible linkages can be obtained by different chemical mechanisms, forexample, covalent binding, affinity binding, intercalation, coordinatebinding and complexation. Preferably, covalent binding is used. Covalentbinding can be achieved either by direct condensation of existing sidechains or by the incorporation of external bridging molecules.

Many bivalent or polyvalent linking agents are useful in couplingprotein molecules, such as an antibody, to other molecules.Representative coupling agents include organic compounds such asthioesters, carbodiimides, succinimide esters, diisocyanates,glutaraldehydes, diazobenzenes and hexamethylene diamines. (See Killenand Lindstrom 1984, "Specific killing of lymphocytes that causeexperimental autoimmune myasthenia gravis by toxin-acetylcholinereceptor conjugates." J. Immunol. 133: 1335-2549; Jansen, F. K., H. E.Blythman, D. Carriere, P. Casella, O. Gros, P. Gros, J. C. Laurent, F.Paolucci, B. Pau, P. Poncelet, G. Richer, H. Vidal, and G. A. Voisin.1982. "Immunotoxins: Hybrid molecules combining high specificity andpotent cytotoxicity." Immunological Rev. 62: 185-216; and Vitetta etal., supra).

B. In Vitro Diagnostics

The different molecules of the present invention can be used tofacilitate diagnosis of calcium-related diseases. Diagnosis can becarried in vitro or in vivo. For example, the molecules of the presentinvention can be used to assay for defects in calcium receptors and theability of a cell to properly respond to extracellular calcium. Cellscan be obtained from patients using standard medical techniques.

Ionomimetics and ionolytics, such as calcimimetics and calcilytics canbe used to assay the responsiveness of a cell or tissue to extracellularcalcium. For example, a tissue or a cell type such as an osteoclast canbe obtained from a patient and treated with a calcimimetic. The cell'sfailure to respond to the calcimimetic indicates a defect in calciumreceptor activity.

Nucleic acids encoding calcium receptors can be used to help determinewhether a particular cellular defect is due to a defective calciumreceptor or at a different point in calcium homeostasis. For example,after a cell defective in calcium homeostasis is identified, a nucleicacid encoding a functional calcium receptor can be inserted into thecell. The ability of the calcium receptor to return calcium homeostasisto normal indicates the defect is due to a calcium receptor.

Nucleic acid probes can be used to identify defects in calcium receptorsoccurring at the genetic level. For example, hybridization probescomplementary to nucleic acid encoding a receptor can be used to clonethe receptor. The cloned receptor can be inserted into a cell, such asan oocyte, and its responsiveness to a calcimimetic or calcilyticdetermined. Another example of using hybridization assay probes todetect defects involves using the probes to detect mRNA levels or thepresence of nucleic acid sequences associated with a particular disease.A decreased mRNA level would be consistent with a decreased amount ofexpressed receptor.

Antibodies and fragments thereof able to recognize a calcium receptorantigen can be used to help determine calcium receptor number,integrity, structure, and to localize cells expressing calcium receptorsin the body. For example, antibodies targeted to calcium receptors canbe used to determine the number of receptors on a cell; antibodies ableto distinguish defective from normal receptors can be used to determinethe presence of defective receptors; antibodies targeted to a calciumreceptor can be used to determine if a disease or surgical procedureresults in the spread of normal or abnormal cells expressing calciumreceptors; and antibodies targeted to a calcium receptor can be used tolocalize cells having abnormal calcium receptor number or structure todirect subsequent treatment.

C. Administration

The different molecules described by the present invention can be usedto treat different diseases or disorders by modulating inorganic ionreceptor activity, preferably calcium receptor activity. The moleculesof the invention can be formulated for a variety of modes ofadministration, including systemic and topical or localizedadministration. Techniques and formulations generally may be found inRemington's Pharmaceutical Sciences, Mack Publishing Co., Easton, Pa.

Suitable dosage forms, in part, depend upon the use or the route ofentry, for example oral, transdermal, or by injection. Such dosage formsshould allow the agent to reach a target cell whether the target cell ispresent in a multicellular host or in culture. For example,pharmacological agents or compositions injected into the blood streamshould be soluble. Other factors are known in the art, and includeconsiderations such as toxicity and dosage form which retard the agentor composition from exerting its effect.

Agents can also be formulated as pharmaceutically acceptable salts(e.g., acid addition salts) and complexes thereof. Pharmaceuticallyacceptable salts are non-toxic salts at the concentration at which theyare administered. The preparation of such salts can facilitate thepharmacological use by altering the physical characteristic of the agentwithout preventing it from exerting its physiological effect. Usefulalterations in physical properties include lowering the melting point tofacilitate transmucosal administration and increasing the solubility tofacilitate administering higher concentrations of the drug.

Pharmaceutically acceptable salts include acid addition salts such asthose containing sulfate, hydrochloride, phosphate, sulfamate, acetate,citrate, lactate, tartrate, methanesulfonate, ethanesulfonate,benzenesulfonate, p-toluenesulfonate, cyclohexylsulfamate and quinate.(See e.g., supra. PCT/US92/03736.) Pharmaceutically acceptable salts canbe obtained from acids such as hydrochloric acid, sulfuric acid,phosphoric acid, sulfamic acid, acetic acid, citric acid, lactic acid,tartaric acid, malonic acid, methanesulfonic acid, ethanesulfonic acid,benzenesulfonic acid, p-toluenesulfonic acid, cyclohexylsulfamic acid,and quinic acid.

Pharmaceutically acceptable salts can be prepared by standardtechniques. For example, the free base form of a compound is dissolvedin a suitable solvent, such as an aqueous or aqueous-alcohol solution,containing the appropriate acid and then isolated by evaporating thesolution. In another example, a salt is prepared by reacting the freebase and acid in an organic solvent.

Carriers or excipients can also be used to facilitate administration ofthe compound. Examples of carriers and excipients include calciumcarbonate, calcium phosphate, various sugars such as lactose, glucose,or sucrose, or types of starch, cellulose derivatives, gelatin,vegetable oils, polyethylene glycols and physiologically compatiblesolvents. The compositions or pharmaceutical composition can beadministered by different routes including intravenously,intraperitoneal, subcutaneous, and intramuscular, orally, topically, ortransmucosally.

For systemic administration, oral administration is preferred.Alternatively, injection may be used, e.g., intramuscular, intravenous,intraperitoneal, and subcutaneous. For injection, the molecules of theinvention are formulated in liquid solutions, preferably inphysiologically compatible buffers such as Hank's solution or Ringer'ssolution. In addition, the molecules may be formulated in solid form andredissolved or suspended immediately prior to use. Lyophilized forms canalso be produced.

Systemic administration can also be by transmucosal or transdermalmeans, or the molecules can be administered orally. For transmucosal ortransdermal administration, penetrants appropriate to the barrier to bepermeated are used in the formulation. Such penetrants are generallyknown in the art, and include, for example, for transmucosaladministration, bile salts and fusidic acid derivatives. In addition,detergents may be used to facilitate permeation. Transmucosaladministration may be through nasal sprays, for example, or usingsuppositories. For oral administration, the molecules are formulatedinto conventional oral administration dosage forms such as capsules,tablets, and liquid preparations.

For topical administration, the molecules of the invention areformulated into ointments, salves, gels, or creams, as is generallyknown in the art.

As shown in the examples provided herein, the amounts of variouscompounds of this invention to be administered can be determined bystandard procedures. Generally, a therapeutically effective amount isbetween about 1 nmole and 3 μmole of the molecule, preferably 0.1 nmoleand 1 μmole depending on its EC₅₀ or IC₅₀ and on the age and size of thepatient, and the disease or disorder associated with the patient.Generally, it is an amount between about 0.1 and 50 mg/kg, preferably0.01 and 20 mg/kg of the animal to be treated.

D. Gene and Oligonucleotide Therapy

Gene and oligonucleotide therapy include the use of nucleic acidencoding a functioning inorganic ion receptor, preferably a calciumreceptor, and the use of inhibitory oligonucleotides. Inhibitoryoligonucleotides include antisense nucleic acids and ribozymes. Gene andoligonucleotide therapy can be performed ex vivo on cells which are thentransplanted into a patient, or can be performed by directadministration of the nucleic acid or nucleic acid-protein complex intothe patient.

A. Antisense Oligonucleotides and Ribozymes

Antisense oligonucleotides and ribozymes are targeted to nucleic acidencoding an inorganic ion receptor, preferably a calcium receptor, andinhibit protein expression from the targeted nucleic acid. Numerousmechanisms have been proposed to explain the effects of antisensenucleic acids. For example, see Helene, C. and Toulme, J. Biochimica etBiophysica Acta 1049:99 (1990), and Uhlmann, E. and Peyman, A. ChemicalReviews 90:543 (1990). Proposed mechanisms include hybridization of anantisense oligonucleotides to nascent mRNA causing prematuretranscription termination and interfering with mRNA processing byhybridizing to a pre-mRNA intron/exon junction. These and several otherproposed mechanisms for inhibiting nucleic acid activity by antisenseoligonucleotide are based upon the ability of antisense nucleic acid tohybridize to a target nucleic acid sequence. Preferably, anti-sensenucleic acids are 15 to 30 bases in length.

Ribozymes are enzymatic RNA molecules capable of catalyzing the specificcleavage of RNA. Ribozyme action involves sequence specific interactionof the ribozyme to complementary target RNA, followed by aendonucleolytic cleavage. Different ribozyme cutting motifs such ashammer-head can be engineered to specifically and efficiently catalyzeendonucleolytic cleavage of specific RNA sequences encoding.

Specific ribozyme cleavage sites include GUA, GUU and GUC. Once cleavagesites are identified, short RNA sequences of between 15 and 20ribonucleotides targeted to the region of the targeted RNA containingthe cleavage site may be evaluated for predicted structural features todetermine ribozyme suitability. The suitability of candidate targets mayalso be evaluated by testing their accessibility to hybridization withcomplementary oligonucleotides, using ribonuclease protection assays.See, Draper PCT WO 93/23569, hereby incorporated by reference herein.

Anti-sense oligonucleotides and ribozymes may be prepared by methodsknown in the art for the synthesis of RNA and DNA molecules. Standardtechniques for chemically synthesizing nucleic acids include solid phasephosphoramidite chemical synthesis. Specific nucleic acids can also beproduced enzymatically using a host transformed with a plasmid encodingfor the desired nucleic acid.

Various modifications to the nucleic acid may be introduced to increaseintracellular stability and half-life. Possible modifications includemodifications to the phosphodiester backbone such as the use ofphosphorothioate or methylphophonate linkages.

Antisense oligonucleotides and ribozymes can be administered to apatient using different techniques such as by naked nucleic acid,nucleic acid compositions (for example, encapsulated by a liposome) andby retroviral vectors. Miller, Nature 357; 455-460, hereby incorporatedby reference herein. Antisense oligonucleotide and ribozymes can also beintroduced into a cell using nucleic acid encoding the antisense nucleicacid or ribozyme.

B. Gene Therapy

Gene therapy can be achieved by transferring a gene encoding aninorganic ion receptor, preferably a calcium receptor, into a patient ina manner allowing expression of the receptor protein. Recombinantnucleic acid molecules encoding receptor protein sequences can beintroduced into a cell in vivo or ex vivo. In vivo transfectiontechniques include the use of liposomes and retroviral vectors. Miller,Nature 357; 455-460, hereby incorporated by reference herein. Ex vivotransfection increases the number of available transfection techniques,but also adds additional complications due to removal and subsequentinsertion of cells into a patient.

E. Transgenic Animals

The present invention also concerns the construction and use oftransgenic animals, and transformed cells encoding inorganic ionreceptors, preferably human calcium receptors. Transgenic animals andtransformed cells can be used to study the effects on cell function ofreceptor excess or depletion. Experimental model systems may be used tostudy the effects in cell or tissue cultures, in whole animals, or inparticular cells or tissues within whole animals or tissue culturesystems. The effects can be studied over specified time intervals(including during embryogenesis).

The present invention provides for experimental model systems forstudying the physiological role of the receptors. Model systems can becreated having varying degrees of receptor expression. For example, thenucleic acid encoding a receptor may be inserted into cells whichnaturally express the receptors such that the gene is expressed at muchhigher levels. Alternatively, a recombinant gene may be used toinactivate the endogenous gene by homologous recombination, and therebycreate an inorganic ion receptor deficient cell, tissue, or animal.

Inactivation of a gene can be caused, for example, by using arecombinant gene engineered to contain an insertional mutation (e.g.,the neo gene). The recombinant gene is inserted into the genome of arecipient cell, tissue or animal, and inactivates transcription of thereceptor. Such a construct may be introduced into a cell, such as anembryonic stem cell, by techniques such as transfection, transduction,and injection. Stem cells lacking an intact receptor sequence maygenerate transgenic animals deficient in the receptor.

Preferred test models are transgenic animals. A transgenic animal hascells containing DNA which has been artificially inserted into a celland inserted into the genome of the animal which develops from thatcell. Preferred transgenic animals are primates, mice, rats, cows, pigs,horses, goats, sheep, dogs and cats.

A variety of methods are available for producing transgenic animals. Forexample, DNA can be injected into the pronucleus of a fertilized eggbefore fusion of the male and female pronuclei, or injected into thenucleus of an embryonic cell (e.g., the nucleus of a two-cell embryo)following the initiation of cell division (Brinster et al., Proc. Nat.Acad. Sci. USA 82.: 4438-4442 (1985)). By way of another example,embryos can be infected with viruses, especially retroviruses, modifiedto carry inorganic ion receptor nucleotide sequences.

Pluripotent stem cells derived from the inner cell mass of the embryoand stabilized in culture can be manipulated in culture to incorporatenucleotide sequences of the invention. A transgenic animal can beproduced from such stem cells through implantation into a blastocystthat is implanted into a foster mother and allowed to come to term.Animals suitable for transgenic experiments can be obtained fromstandard commercial sources such as Charles River (Wilmington, Mass.),Taconic (Germantown, N.Y.), and Harlan Sprague Dawley (Indianapolis,Ind.).

Methods for the culturing of embryonic stem (ES) cells and thesubsequent production of transgenic animals by the introduction of DNAinto ES cells using methods such as electroporation, calciumphosphate/DNA precipitation and direct injection also are well known tothose of ordinary skill in the art. See, for example, Teratocarcinomasand Embryonic Stem Cells, A Practical Approach, E. J. Robertson, ed.,IRL Press (1987).

Procedures for embryo manipulations are well known in the art. Theprocedures for manipulation of the rodent embryo and for microinjectionof DNA into the pronucleus of the zygote are well known to those ofordinary skill in the art (Hogan et al., supra). Microinjectionprocedures for fish, amphibian eggs and birds are detailed in Houdebineand Chourrout, Experientia 47:897-905 (1991). Other procedures forintroduction of DNA into tissues of animals are described in U.S. Pat.No. 4,945,050 (Sandford et al., Jul. 30, 1990).

Transfection and isolation of desired clones can be carried out usingstandard techniques (e.g., E. J. Robertson, supra). For example, randomgene integration can be carried out by co-transfecting the nucleic acidwith a gene encoding antibiotic resistance. Alternatively, for example,the gene encoding antibiotic resistance is physically linked to anucleic acid sequence encoding an inorganic ion receptor.

DNA molecules introduced into ES cells can also be integrated into thechromosome through-the process of homologous recombination. Capecchi,Science 244: 1288-1292 (1989). Methods for positive selection of therecombination event (e.g., neomycin resistance) and dualpositive-negative selection (e.g., neomycin resistance and gancyclovirresistance) and the subsequent identification of the desired clones byPCR have been described by Capecchi, supra and Joyner et al., Nature338:153-156 (1989), the teachings of which are incorporated herein.

The final phase of the procedure is to inject targeted ES cells intoblastocysts and to transfer the blastocysts into pseudopregnant females.The resulting chimeric animals are bred and the offspring are analyzedby Southern blotting to identify individuals that carry the transgene.

An example describing the preparation of a transgenic mouse is asfollows. Female mice are induced to superovulate and placed with males.The mated females are sacrificed by CO₂ asphyxiation or cervicaldislocation and embryos are recovered from excised oviducts. Surroundingcumulus cells are removed. Pronuclear embryos are then washed and storeduntil the time of injection.

Randomly cycling adult female mice paired with vasectomized males serveas recipients for implanted embryos. Recipient females are mated at thesame time as donor females and embryos are transferred surgically torecipient females.

The procedure for generating transgenic rats is similar to that of mice.See Hammer et al., Cell 63:1099-1112 (1990). Procedures for theproduction of transgenic non-rodent mammals and other animals are knownin art. See, for example, Houdebine and Chourrout, supra; Pursel et al.,Science 244:1281-1288 (1989); and Simms et al., Bio/Technology 6:179-183(1988).

F. Transfected Cells Lines

Nucleic acid expressing a functional inorganic ion receptor can be usedto create transfected cells lines which functionally express a specificinorganic ion receptor. Such cell lines have a variety of uses such asbeing used for high-throughput screening for molecules able to modulateinorganic ion receptor activity, preferably calcium receptor activity;and being used to assay binding to an inorganic ion receptor, preferablya calcium receptor.

A variety of cell lines are capable of coupling exogenously expressedreceptors to endogenous functional responses. A number of these celllines (e.g., NIH-3T3, HeLa, NG115, CHO, HEK 293 and COS7) can be testedto confirm that they lack an endogenous calcium receptor. Those lineslacking a response to external Ca²⁺ can be used to establish stablytransfected cell lines expressing the cloned calcium receptor.

Production of these stable transfectants is accomplished by transfectionof an appropriate cell line with a eukaryotic expression vector, such aspMSG, in which the coding sequence for the calcium receptor cDNA hasbeen cloned into the multiple cloning site. These expression vectorscontain a promoter region, such as the mouse mammary tumor viruspromoter (MMTV), that drive high-level transcription of cDNAs in avariety of mammalian cells. In addition, these vectors contain genes forthe selection of cells that stably express the cDNA of interest. Theselectable marker in the pMSG vector encodes an enzyme, xanthine-guaninephosphoribosyl transferase (XGPRT), that confers resistance to ametabolic inhibitor that is added to the culture to kill thenontransfected cells. A variety of expression vectors and selectionschemes are usually assessed to determine the optimal conditions for theproduction of calcium receptor-expressing cell lines for use inhigh-throughput screening assays.

The most effective method for transfection of eukaryotic cell lines withplasmid DNA varies with the given cell type. The calcium receptorexpression construct will be introduced into cultured cells by theappropriate technique, either Ca²⁺ phosphate precipitation, DEAE-dextrantransfection, lipofection or electroporation.

Cells that have stably incorporated the transfected DNA will beidentified by their resistance to selection media, as described above,and clonal cell lines will be produced by expansion of resistantcolonies. The expression of the calcium receptor cDNA by these celllines will be assessed by solution hybridization and Northern blotanalysis. Functional expression of the receptor protein will bedetermined by measuring the mobilization of intracellular Ca²⁺ inresponse to externally applied calcium receptor agonists.

The following examples illustrate the invention, but do not limit itsscope.

EXAMPLES

In the studies described herein, a variety of organic molecules werefound to mobilize intracellular Ca²⁺ and depress PTH secretion inparathyroid cells. These molecules are structurally diverse, but mosthave a net positive charge at physiological pH. The cationic nature ofthe organic molecules plays an important role, but is not the solefactor determining activity.

Example 1 Screening Calcimimetic Molecules on Bovine Parathyroid Cells

Dissociated bovine parathyroid cells were purified on gradients ofPercoll and cultured overnight in serum-free medium. The cells weresubsequently loaded with fura-2 and the concentration of freeintracellular Ca²⁺ measured fluorimetrically. Changes in Ca²⁺ !_(i) wereused to screen for molecules active at the calcium receptor. To beconsidered a calcimimetic in this example, a molecule was required toshow the normal effects caused by increasing extracellular Ca²⁺ andtriggered by the activation of the calcium receptor. That is,

1) The molecule must elicit an increase in Ca²⁺ !_(i) ; the increase inCa²⁺ !_(i) may persist in the absence of extracellular Ca²⁺ and/or themolecule may potentiate increases in Ca²⁺ !_(i) elicited byextracellular Ca²⁺.

2) The molecule must cause a decrease in isoproterenol-stimulated cyclicAMP formation which is blocked by pertussis toxin;

3) The molecule must inhibit PTH secretion over the same range ofconcentrations that cause the increase in Ca²⁺ !_(i) ; and

4) The concentration-response curves for increases in Ca²⁺ !_(i) and PTHsecretion by the molecule must be shifted to the right by a PKCactivator, such as phorbol myristate acetate (PMA).

Several structurally different classes of molecules were tested:polyamines, aminoglycoside antibiotics, protamine, and polymers oflysine or arginine. The structures of these molecules are depicted inFIG. 1. Included in FIG. 1 are the net positive charge of the moleculesand their EC₅₀ 's for evoking the mobilization of intracellular Ca²⁺ inbovine parathyroid cells.

In general, the greater the net positive charge on the molecule, thegreater its potency in causing the mobilization of intracellular Ca²⁺.However, some striking exceptions to this apparent general rule havebeen found as discussed below.

As can be seen from the figures, spermine, neomycin B, and protamineevoked rapid and transient increases in Ca²⁺ !_(i) in fura-2-loadedbovine parathyroid cells (FIGS. 6, 7, 11). They did not, however, causesustained, steady-state increases in Ca²⁺ !_(i) in bovine parathyroidcells (FIG. 6, 11), although they did in human parathyroid cells (FIG.19). In this respect, they resembled the cytosolic Ca²⁺ responseelicited by extracellular Mg²⁺, which causes the mobilization ofintracellular Ca²⁺ unaccompanied by an influx of extracellular Ca²⁺ inbovine cells (FIG. 11b). Transient increases in Ca²⁺ !_(i) elicited byspermine, neomycin B, or protamine were not blocked by lowconcentrations (1 μM) of La³⁺ or Gd³⁺ (FIG. 11f,g). Cytosolic Ca²⁺transients elicited by the molecular polycations persisted in theabsence of extracellular Ca²⁺, but were blocked when cellular stores ofCa²⁺ were depleted by pretreatment with ionomycin (FIGS. 7, 11h and11i.). All of these molecules therefore cause the mobilization ofintracellular Ca²⁺ in parathyroid cells.

It was additionally shown that the molecular polycations mobilized thesame pool of intracellular Ca²⁺ as that used by extracellular Ca²⁺.Thus, increasing the concentration of extracellular Ca²⁺ progressivelyinhibited the transient increases in Ca²⁺ !_(i) evoked by spermine (FIG.6). Conversely, a maximally effective concentration of spermine orneomycin B (FIG. 12) blocked transient, but not steady-state increasesin Ca²⁺ !_(i) evoked by extracellular Ca²⁺.

Significantly, spermine, neomycin B, and protamine inhibited PTHsecretion to the same extent as extracellular Ca²⁺. These inhibitoryeffects on secretion were obtained at concentrations that caused themobilization of intracellular Ca²⁺ (FIGS. 8, 13). These findings arerelevant to understanding the mechanisms contributing to the regulationof PTH secretion by extracellular Ca²⁺. Because a variety of inorganicpolycations all inhibit secretion, yet only extracellular Ca²⁺ causessustained, steady-state increases in Ca²⁺ !_(i), such increases in Ca²⁺!_(i) cannot be importantly involved in the regulation of secretion.Mobilization of intracellular Ca²⁺, rather than the influx ofextracellular Ca²⁺, is the essential mechanism associated with theinhibition of PTH secretion. This is important because it defines thesufficient mechanism to be affected if a molecule is to affect PTHsecretion; molecules stimulating selectively the influx of extracellularCa²⁺ will be relatively ineffective in suppressing PTH secretion. Incontrast, molecules causing solely the mobilization of intracellularCa²⁺ should be just as efficacious as extracellular Ca²⁺ in suppressingPTH secretion.

Like the mobilization of intracellular Ca²⁺ elicited by extracellularCa²⁺, that elicited by molecular polycations was depressed by PMA. Arepresentative experiment showing the preferential inhibitory effects ofPMA on cytosolic Ca²⁺ transients elicited by spermine is shown in FIG.14. Cytosolic Ca²⁺ transients evoked by ATP were unaffected, even when asubmaximal concentration of ATP was used. The effect of PMA on cytosolicCa²⁺ transients elicited by the molecular polycations paralleled itseffect on responses to extracellular Ca²⁺ ; in both cases, there was ashift to the right in the concentration-response curve (FIG. 15). Thedepressive effects of PMA on Ca²⁺ !_(i) were accompanied by potentiatingeffects on secretion which were overcome at higher concentrations of theorganic polycations (FIG. 16).

The mobilization of intracellular Ca²⁺ elicited by molecular polycationswas associated with increases in the formation of inositol phosphates.For example, protamine caused a rapid (within 30 seconds) increase inthe formation of IP₃ which was accompanied by a rise in levels of IP₁.Both these affects were dependent on the concentration of extracellularprotamine (FIG. 17). Moreover, pretreatment with PMA blunted theformation of inositol phosphates elicited by molecular polycations.Representative results obtained with spermine are presented in FIG. 18.

Spermine, neomycin B, and protamine depressed isoproterenol-inducedincreases in cyclic AMP. Like the inhibitory effects of extracellularCa²⁺ on cyclic AMP formation, those caused by molecular polycations wereblocked by pretreatment with pertussis toxin (Table 2).

                  TABLE 2                                                         ______________________________________                                                        cyclic AMP (% of control)                                                     control +PTx                                                  ______________________________________                                        0.5 mM Ca.sup.2+  100       106 ± 8                                        2.0 mM Ca.sup.2+  19 ± 4 94 ± 2                                         0.5 mM Ca.sup.2+, 200 μM spermine                                                            23 ± 5 93 ± 6                                         0.5 mM Ca.sup.2+, 30 μM neomycin B                                                           28 ± 8 87 ± 6                                         0.5 mM Ca.sup.2+, 2 μg/ml protamine                                                          20 ± 4 89 ± 9                                         ______________________________________                                    

Pertussis toxin (PTx) blocks the inhibitory effects of extracellularCa²⁺ and molecular polycations on cyclic AMP formation. Bovineparathyroid cells were cultured for 16 hours with or without 100 ng/mlpertussis toxin. The cells were subsequently washed and incubated for 15min with 10 μM isoproterenol with or without the indicatedconcentrations of extracellular Ca²⁺ or molecular polycations. Totalcyclic AMP (cells+supernatant) was determined by RIA and the results areexpressed as a percentage of the levels obtained in 0.5 mM Ca²⁺ (112±17pmole/10⁶ cells). Each value is the mean±SEM of three experiments.

In human parathyroid cells, extracellular Mg²⁺ elicited a sustained,steady-state increase in Ca²⁺ !_(i) in addition to a rapid transientincrease (FIG. 10 ). As in bovine parathyroid cells responding toextracellular Ca²⁺, the steady-state increase in Ca²⁺ !_(i) evoked byMg²⁺ in human parathyroid cells results from Ca²⁺ influx throughvoltage-insensitive channels (FIG. 10a). This effect of Mg²⁺ onsteady-state Ca²⁺ !_(i) in human parathyroid cells is seen in bothadenomatous and hyperplastic tissue.

Neomycin B and spermine were tested for effects on Ca²⁺ !_(i) in humanparathyroid cells prepared from adenomatous tissue. Representativeresults with neomycin B are shown in FIG. 19. Neomycin B caused not onlya transient, but additionally a steady-state increase in Ca²⁺ !_(i) inhuman parathyroid cells (FIG. 19a). Thus, in human cells, the pattern ofchange in Ca²⁺ !_(i) evoked by extracellular Ca²⁺, Mg²⁺ or neomycin B isvery similar.

Cytosolic Ca²⁺ transients elicited by neomycin B persisted in thepresence of La³⁺ (1 μM) and absence of extracellular Ca²⁺. Neomycin Btherefore causes the mobilization of intracellular Ca²⁺ in humanparathyroid cells. Neomycin B inhibited PTH secretion from humanparathyroid cells at concentrations that caused the mobilization ofintracellular Ca²⁺ (FIG. 13). There were, however, some differences inthe responses of human and bovine parathyroid cells to neomycin B. TheEC₅₀ of neomycin B for the mobilization of intracellular Ca²⁺ was 40 μMin bovine and 20 μM in human parathyroid cells (cf. FIGS. 13 and 15),whereas the potency of spermine was similar in bovine and humanparathyroid cells (EC₅₀ =150 μM). Thus, although bovine cells can beused for initial studies to screen test molecules for activity, it isimportant to perform follow-up studies using human parathyroid cells.

To assess the effects of molecular polycations on C-cells, a neoplasticcell line, derived from a rat medullary thyroid carcinoma (rMTC 6-23cells) was used. Both spermine (10 mM) and neomycin B (5 mM) werewithout effect on basal Ca²⁺ !_(i) in these cells. Nor did eithermolecule affect the response to the subsequent addition of extracellularCa²⁺. Representative results documenting the lack of effect of neomycinB are shown in FIG. 21. Neomycin B (1 mM) or spermine (1 or 5 mM) failedto evoke any increase in Ca²⁺ !_(i) in osteoclasts (FIG. 23). In thetrace shown, there appeared to be some potentiation of the response to asubsequent increase in the concentration of extracellular Ca²⁺, althoughthis was not a consistent finding. In two other cells, spermine (5 mM)was again without effect on basal Ca²⁺ !_(i) and caused a smallinhibition (about 15%) of the extracellular Ca²⁺ -induced increase inCa²⁺ !_(i). In a third cell, neomycin B (5 mM) was without effect onbasal Ca²⁺ !_(i) and did not affect increases in Ca²⁺ !_(i) elicited byextracellular Ca²⁺. The overall picture that develops from these studiesis that spermine and neomycin B are without effect on basal orstimulated levels of cytosolic Ca²⁺ in osteoclasts.

The failure of the molecular polycations to affect the Ca²⁺ -sensingmechanisms of C-cells or osteoclasts demonstrates the ability todiscover or design novel lead molecules that act specifically on theparathyroid cell calcium receptor or otherwise modulate one or morefunctions of the parathyroid cell's normal response to Ca²⁺ !_(i).

Screening of various other molecules is described in detail below andthe results summarized in Table 1.

Example 2 Polyamine Screening

Straight-chain polyamines (Spermine, spermidine, TETA, TEPA, and PEHA)and two derivatives thereof (NPS 381 and NPS 382) were screened as inExample 1. These molecules were all found to mobilize intracellular Ca²⁺in bovine parathyroid cells. Their order of potency is as follows, withthe net positive charge listed in parentheses:

                  TABLE 3                                                         ______________________________________                                        Molecule        EC.sub.50 (in μM)                                          ______________________________________                                        NPS 382 (+8)    50                                                            NPS 381 (+10)   100                                                           spermine (+4)   150                                                           PEHA (+6)       500                                                           spermidine (+3) 2000                                                          TEPA (+5)       2500                                                          TETA (+4)       8000                                                          ______________________________________                                    

Putrescine (+2) and cadaverine (+2) were inactive at a concentration of2 mM.

Another straight-chain polyamine, DADD, behaved somewhat differentlyfrom the other polyamines and is described in Example 7.

Example 3 Cyclic Polyamine Screening

Two cyclic polyamines, hexacyclen and NPS 383, were screened as inExample 1. Hexacyclen (+6, EC₅₀ =20 μM) is 7-fold more potent than NPS383 (+8, EC₅₀ =150 μM). The converse would be expected based solely onnet positive charge as the structural characteristic for calciumreceptor activity.

Example 4 Aminoglycoside Antibiotic Screening

Six antibiotics were screened as in Example 1. The resulting EC₅₀ 's forthe mobilization of intracellular Ca²⁺, in rank order of potency, were:

                  TABLE 4                                                         ______________________________________                                        Antibiotic      EC.sub.50 (in μM)                                          ______________________________________                                        neomycin (+6)   10                                                            gentamicin (+5) 150                                                           bekanamycin (+5)                                                                              200                                                           streptomycin (+3)                                                                             600                                                           ______________________________________                                    

Kanamycin (+4.5) and lincomycin (+1) were without effect at aconcentration of 500 μM. Within the aminoglycoside series, there is acorrelation between net positive charge and potency. However, neomycinis considerably more potent than various polyamines (NPS 381, NPS 382,NPS 383, PEHA) that have an equal or greater positive charge. Sinceaminoglycoside antibiotics of this type have renal toxicity which may berelated to interaction with calcium receptors in the kidney, suchscreening could be used to screen for toxicity in the development of newaminoglycoside antibiotics.

Example 5 Peptide and Polamino Acid Screening

Protamine and polymers of lysine or arginine varying in peptide lengthwere screened for their ability to mobilize intracellular Ca²⁺ as inExample 1. The resulting EC₅₀ 's for the mobilization of intracellularCa²⁺, in rank order of potency, were:

                  TABLE 5                                                         ______________________________________                                        Peptide (MW in kD)                                                                            EC.sub.50 (in nM)                                             ______________________________________                                        polyArq (100)   4                                                             polyArg (40)    15                                                            polyLys (27)    30                                                            protamine (4.8) 75                                                            polyArgTyr (22) 200                                                           polyLys (14)    1000                                                          polyLys (3.8)   3000                                                          ______________________________________                                    

The net positive charge of these polymers increases as the MW increases.Thus, as for the aminoglycosides, there is a direct correlation betweennet charge and potency among this series of polyamino acids. Protamineis essentially polyArg with a net positive charge of +21.

Example 6 Arylalkyl Polyamine Screening

Molecules selected from the class of arylalkyl polyamines derived fromthe venoms of wasps and spiders were screened as in Example 1.

Philanthotoxin-433 (+3) was without effect at a concentration of 500 μM.It is similar in structure to the argiotoxins described below.

Argiotoxin-636 (400 μM) did not elicit increases in Ca²⁺ !, but it didpotentiate cytosolic Ca²⁺ responses to the subsequent addition ofextracellular Ca²⁺. This is a feature common to all molecules thatactivate the calcium receptor and is also seen with a variety ofextracellular divalent cations. This is considered in more detail inExample 7.

In contrast to argiotoxin-636, argiotoxin-659 elicited increases in Ca²⁺!_(i) with an EC₅₀ of 300 μM. Argiotoxin-659 differs from argiotoxin-636in having a 4-hydroxyindole moiety rather than a 2,4-dihydroxyphenylgroup. This is the only structural difference between these twomolecules. Thus, the difference in potency lies in the nature of thearomatic group, not in the polyamine chain which carries the positivecharge.

Example 7 Screening of Ca²⁺ Channel Blockers

Ca²⁺ channel blockers, i.e., those molecules which block influx ofextracellular Ca²⁺ through voltage-sensitive Ca²⁺ channels, werescreened as in Example 1. There are three structural classes of Ca²⁺channel blockers: (1) dihydropyridines, (2) phenylalkylamines, and (3)benzothiazipines.

None of the dihydropyridines tested (nifedipine, nitrendipine, BAY K8644, and (-) 202-791 and (+) 202-791) had any effect on basal Ca²⁺!_(i) or increases in Ca²⁺ !_(i) evoked by extracellular Ca²⁺ when theywere tested at 1 μM. Previous studies showed that parathyroid cells lackvoltage-sensitive Ca²⁺ channels, but do have voltage-insensitive Ca²⁺channels that are regulated by the calcium receptor.

The phenylalkylamines examined were verapamil, D-600 (a methoxyderivative of verapamil), TMB-8, and an analog of TMB-8, NPS 384. Thefirst three molecules were tested at a concentration of 100 μM. Thephenylalkylamines behaved differently from other molecules examined.They evoked no change in Ca²⁺ !_(i) when added to cells bathed in buffercontaining a low concentration of extracellular Ca²⁺ (0.5 mM). However,verapamil, D-600, and TMB-8 potentiated the mobilization ofintracellular Ca²⁺ elicited by extracellular divalent cations and theyadditionally blocked the influx of extracellular Ca²⁺. At intermediatelevels of extracellular Ca²⁺ (1-1.5 mM), these molecules were capable ofevoking a small, but robust increase in Ca²⁺ !_(i) that arose from themobilization of intracellular Ca²⁺.

The phenylalkylamines act differently than organic polycations likeneomycin. The data suggest that verapamil, D-600 and TMB-8 are partialagonists or allosteric activators at the calcium receptor, in contrastto the other molecules examined which are full agonists.

Molecule NPS 384, at a concentration of 300 μM, did not evoke anincrease in Ca²⁺ !_(i), but it blocked influx of extracellular Ca²⁺.Testing at higher concentrations may reveal an ability of this moleculeto cause the mobilization of intracellular Ca²⁺.

While the ability of these molecules to block influx is intriguing andnot entirely unexpected, it is the ability of these molecules to evoketransient increases in Ca²⁺ !_(i) (arising from intracellular Ca²⁺mobilization) that is important. Considerable experience withmeasurements of Ca²⁺ !_(i) in parathyroid cells shows that transientincreases in Ca²⁺ !_(i) almost invariably result from the mobilizationof intracellular Ca²⁺ and therefore reflects activation of the calciumreceptor.

The benzothiazipine examined, diltiazem, was similar in all respects toverapamil and D-600 and was also effective at 100 μM.

With the exception of the phenylalkylamines, all the active moleculestested above evoke increases in Ca²⁺ !_(i) having a magnitude similar tothat evoked by a maximally effective concentration of extracellularCa²⁺. This shows that these molecules are equally efficacious asextracellular divalent cations. This contrasts with the activity ofphenylalkylamines, which seem to act only as partial agonists.

Amongst the phenylalkylamines, some interesting structure-activityrelationships emerge. Significant is the different potencies ofmolecules like TMB-8 and NPS 384. TMB-8 potentiated transient increasesin Ca²⁺ !_(i) at 100 μM whereas NPS 384 fails to do so even at 300 μM,yet these molecules carry the same net positive charge. It follows thatsome other structural feature, unrelated to net charge, imparts greaterpotency to TMB-8.

Example 8 Molecule Screening on Human Parathyroid Cells

Spermine and neomycin were tested for effects on Ca²⁺ !_(i) in humanparathyroid cells obtained from glands removed by surgery and preparedas in Example 1. In human parathyroid cells, spermine was found to causeonly a small increase in Ca²⁺ !_(i) when tested at a concentration of300 μM.

Neomycin, on the other hand, evoked a large increase in Ca²⁺ !_(i) inhuman parathyroid cells when tested at a concentration of 20 μM. Themagnitude of the response elicited by neomycin was equal to that evokedby a maximally effective concentration of extracellular Ca²⁺.

Example 9 Molecule Screening on Xenopus Oocytes

Oocytes injected with mRNA from human parathyroid cells express thecalcium receptor and mobilize intracellular Ca²⁺ in response to avariety of extracellular inorganic di- and trivalent cations. Using thisscreen allows one to test for an action directly on the calciumreceptor. Oocytes expressing the calcium receptor also responded toseveral molecules active on intact parathyroid cells when screened asfollows. Hexacyclen caused the mobilization of intracellular Ca²⁺ at aconcentration of 135 μM. Neomycin (100 μM) and NPS 382 (5 mM) were alsoeffective. This offers rather compelling evidence showing that thesemolecules act on the calcium receptor or on some other proteinintimately associated with its function.

For example, we have been able to detect calcium receptor expression inoocytes by measuring ⁴⁵ Ca²⁺ mobilization. In these experiments, oocyteswere injected with bovine parathyroid mRNA or water and, after 72 hours,exposed to serum or 10 mM neomycin. Prior to being stimulated, oocyteswere loaded with ⁴⁵ Ca² +. Stimulation with serum for 20 min resulted inintracellular ⁴⁵ Ca²⁺ release representing a 45% increase compared tomock challenge with buffer. Challenge with 10mM neomycin for 20 minresulted in a 76% increase in ⁴⁵ Ca²⁺ release. The assay is sensitiveenough for use in cloning the calcium receptor, and has the advantage ofa higher throughput than the electrophysiological measurement of Ca²⁺-activated Cl⁻ current.

In another example, human osteoclastoma tissue was obtained from bonebiopsy tissue. Oocytes injected with mRNA isolated from this tissue werechallenged with 30 mM Ca²⁺. Controls did not respond while 8 of 12oocytes injected with osteoclastoma mRNA responded appropriately (FIG.34). These experiments provide the first evidence that the Ca²⁺ responseof osteoclasts to extracellular Ca²⁺ is in fact genetically encoded. Theresults also indicate that the osteoclast calcium receptor may be clonedby expression in Xenopus oocytes.

Example 10 Molecule Screening on Rat Osteoclasts

The different sensitivities of parathyroid cells and rat osteoclasts toextracellular Ca²⁺ suggest that their calcium receptors are different.While parathyroid cells respond to extracellular Ca²⁺ concentrationsbetween 0.5 and 3 mM, osteoclasts respond only when the level ofextracellular Ca²⁺ increases beyond 5 mM. This rather high concentrationof Ca²⁺ is nonetheless physiological for osteoclasts; as they resorbbone, the local concentration of extracellular Ca²⁺ may reach levels ashigh as 30 mM.

Molecule screening with rat osteoclasts was performed as follows.Osteoclasts were obtained from the long bones of neonatal rats. Ca²⁺!_(i) was measured in single cells using the fluorimetric indicatorindo-1. Spermine, spermidine, neomycin, and verapamil were tested, andnone of these caused any large increase in Ca²⁺ !_(i) in osteoclasts(although small responses were detected).

At a concentration of 1 mM, spermidine caused a small increase in Ca²⁺!_(i) (about 10% of that evoked by a maximal concentration ofextracellular Ca²⁺). Neither neomycin (10 mM) nor spermine (10 or 20 mM)caused increases in Ca²⁺ !_(i) in rat osteoclasts. Neomycin (10mM) didnot block the increase in Ca²⁺ !_(i) elicited by the subsequent additionof 25 mM extracellular Ca²⁺. Pretreatment with spermine (20 mM),however, did depress the response to extracellular Ca²⁺. Verapamil (100μM) caused no detectable increase in Ca²⁺ !_(i), but it did block theresponse to extracellular Ca²⁺.

Comparisons between osteoclasts and parathyroid cells show thatmolecules active on the latter are relatively ineffective inosteoclasts. This demonstrates that drugs that target a specific calciumreceptor without affecting those receptor types present on other Ca²⁺-sensing cells are readily developed. Similarly, drugs active at two ormore such calcium receptors may also be developed.

Screening for Calcimimetic and Calcilytic Activity on the OsteoclastCalcium Receptor

Compounds possessing activity on the osteoclast calcium receptor can bediscovered by measuring Ca²⁺ !_(i) in single rat osteoclasts asdescribed above. An improved assay enables moderate-to-high levels ofcompound throughput. This new method is based on the use of rabbitosteoclasts which can be obtained in high yield (10⁵ per animal) andpurity (95% of the cells are osteoclasts). The purity of the rabbitosteoclast preparation allows measurements of Ca²⁺ !_(i) to be performedon populations of cells. Because the recorded fluorescence signal is anaveraged population response, intercellular variability is minimized andthe precision of the assay is greatly increased. This, in turn, enablesmore compounds to be screened for activity.

Rabbit osteoclasts are prepared from 6-day old bunnies. The animals aresacrificed by decapitation and the long bones removed and placed intoosteoclast medium (OC medium: alpha-minimum essential medium containing5% fetal bovine serum and penicillin/streptomycin). The bones are cutinto sections with a scalpel and placed in 2 ml of OC media in a 50-mlconical centrifuge tube. The bone sections are minced with scissorsuntil a fairly homogeneous suspension of bone particles is obtained. Thesuspension is then diluted with 25 ml of OC media and the preparationswirled gently ("vortexed") for 30 seconds. The bone particles areallowed to settle for 2 minutes after which the supernatant is removedand added to a 50-ml centrifuge tube. The bone particles are resuspendedin OC media, swirled, sedimented and harvested as just described. Thesupernatants from the two harvests are combined and centrifuged and theresulting cellular pellet resuspended in Percoll. The suspension is thencentrifuged and the white viscous band just below the meniscus isremoved and washed with OC media. The Percoll centrifugation stepresults in a significant improvement in purity and allows osteoclasts tobe plated at high densities, suitable for measuring Ca²⁺ !_(i) inpopulations of cells. The cells are plated onto glass cover slipsappropriate for measuring Ca²⁺ !_(i) according to one of the methodsdescribed below. If necessary, the purity of the preparation can beimproved. In this case, the cells are cultured overnight and then rinsedwith Ca²⁺ - and Mg²⁺ -free buffer. The cell monolayer is then immersedin Ca²⁺ - and Mg²⁺ -free buffer containing 0.02% EDTA and 0.001% pronasefor 5 minutes. This buffer is then removed and replaced with OC mediaand the cells allowed to recover for 1 to 2 hours before loading thecells with fluorimetric indicator and measuring Ca²⁺ !_(i) as describedbelow.

In one embodiment, this technique allows the measurement of Ca²⁺ !_(i)in populations of osteoclasts using fluorescence microscopy. Thepurified osteoclasts are allowed to attach to 25-mm diameter glass coverslips and then loaded with indo-1. The cover slips are secured into asuperfusion chamber and placed onto the stage of a fluorescencemicroscope. The use of a low-power objective (×4) allows a fieldcontaining 10 to 15 osteoclasts to be visualized. In one variation, thefluorescence of each cell in the field can be recorded simultaneouslyand stored separately for later analysis. Changes in Ca²⁺ !_(i) of eachcell can be estimated and the average response of all cells in the fieldcalculated. In another variation, the fluorescence from the entire fieldof cells can be recorded and processed immediately. In either variation,the final data are in the form of an average response from the cellspresent in the microscopic field. Because of this, intercellularvariability is minimized and precision of the assay greatly increased.This method enables 10-20 compounds per week to be screened for activityon the osteoclast calcium receptor.

In a more preferred embodiment, this technique allows the measurement ofCa²⁺ !_(i) in populations of osteoclasts using a conventionalfluorimeter. The purified osteoclasts are allowed to attach torectangular glass cover slips. In one variation, a standard quartzcuvette (1 cm²) is used and the glass coverslips are 2×1.35 cm. Inanother variation, a microcuvette is used (0.5 cm²) and the glasscoverslips are 1×0.75 cm. In either case the cells are loaded withfura-2 or some other suitable fluorimetric indicator for measuring Ca²⁺!_(i). The fluorescence of indicator-loaded cells is recorded asdescribed above for bovine parathyroid cells. This method allows ahigher throughput than fluorescence microscopy and enables 20-50compounds per week to be evaluated for activity on the osteoclastcalcium receptor.

In a most preferred embodiment, the technique can be used to measureCa²⁺ !_(i) in osteoclasts in a 96-well plate. The purified osteoclastsare plated at high density into each well of a 96-well plate andsubsequently loaded with a suitable fluorimetric indicator. Thefluorescence of each well is recorded using a custom-designedfluorimeter attached to a Hamilton 220 robotic liquid handler. Thismethod is the fully automated and is capable of reading 1,000 compoundper week per device.

Example 11 Calcium Receptor Selectivity

This example demonstrates that calcium receptors present on differentcells exist as distinct subtypes which can be differentially affected bya particular drug. The parathyroid cell calcium receptor senses levelsof extracellular Ca²⁺ around 1.5 mM whereas the calcium receptor on theosteoclast responds to levels around 10 mM (FIG. 22). Neomycin orspermine, which activate the parathyroid cell calcium receptor, fail toaffect the calcium receptors on C-cells or osteoclasts (FIGS. 21 and23).

These data constitute the first evidence for pharmacologically distinctsubtypes of calcium receptors and these data are being used to designand develop drugs that act selectively on a particular type of calciumreceptor. Indeed, testing of lead molecules demonstrate suchcell-specific effects. For example, Mg²⁺, which increases Ca²⁺ !_(i) inbovine parathyroid cells (EC₅₀ =5 mM), is without effect on Ca²⁺ !_(i)in osteoclasts even when tested at concentrations as high as 30 mM.Conversely, R-fendiline, which activates the parathyroid cell calciumreceptor, is effective in activating the osteoclast calcium receptoronly at concentrations 10-fold higher. Finally, agatoxin 489, althoughnot very potent in activating the C-cell calcium receptor (EC₅₀ =150μM), is a quite potent activator of the parathyroid cell calciumreceptor (EC₅₀ =3 μM). The lead molecules presently under developmentwill affect selectively the activity of a specific type of Ca²⁺ -sensingcell in vivo.

Drugs with less specificity might not necessarily be therapeuticallyundesirable. Thus, depressing osteoclast activity and stimulatingcalcitonin secretion are two different approaches to inhibiting boneresorption. Drugs that target the calcium receptors on both of thesecells might be very effective therapies for osteoporosis. Because PTH isalso involved in regulating bone metabolism, drugs acting on theparathyroid cell calcium receptor may also be useful in the treatmentand/or prevention of osteoporosis.

Results of some test molecules are shown below. In Table 6, thecomparative activity of calcimimetic molecules is shown. Bovineparathyroid cells and C-cells (rMTC 6-23 cells) were loaded with fura-2,and rat osteoclasts with indo-1 and the potency of the indicatedmolecules to mobilize intracellular Ca²⁺ determined by constructingcumulative concentration-response curves. Molecules listed as "inactive"did not alter Ca²⁺ !_(i) when tested at a concentration of 1 mM.

                  TABLE 6                                                         ______________________________________                                                EC.sub.50 (μM)                                                     COMPOUND  PARATHYROID  OSTEOCLAST  C-CELL                                     ______________________________________                                        NPS R-568 0.60         200         1.9                                        NPS S-568 30           --          --                                         NPS R-467 2            >100        2.2                                        NPS S-467 >30          --          --                                         NPS 017   6            inactive    150                                        R-Fendiline                                                                             9            150         --                                         Fendiline*                                                                              15           200         >100                                       NPS 015   22           --          inactive                                   NPS 019   40           >300        5                                          R-Prenylamine                                                                           7            150         6                                          1H*       30           250         --                                         Spermine  150          inactive    inactive                                   Neomycin  40           inactive    inactive                                   ______________________________________                                         *racemic mixture; "inactive" is defined as causing no increase in             cytosolic Ca.sup.2+ at a concentration of 1.5 mM.                        

Example 12 Lead Molecules for Parathyroid Calcium Receptor

Structure-activity studies using polyamines and arylalkyl polyamines ledto the testing of molecules structurally akin to fendiline. Fendiline isa potent activator of the parathyroid cell calcium receptor. Thismolecule is notable because it possess only one positive charge, yet ismuch more potent than many polybasic molecules. Brief (2 min)pretreatment with PMA shifts the concentration-response curve forfendiline to the right. This indicates that fendiline acts through thesame mechanism used by extracellular Ca²⁺ to activate the calciumreceptor on parathyroid cells.

Fendiline evokes the mobilization of intracellular Ca²⁺ in Xenopusoocytes expressing the parathyroid cell calcium receptor, whichdemonstrates a direct action on the calcium receptor (FIG. 33).Moreover, fendiline contains a chiral carbon, and therefore exists intwo isomeric forms. Both isomers have been synthesized and examined foractivity. The R-isomer, R-fendiline, is 12 times more potent than theS-isomer, S-fendiline. This is the first demonstration that a calciumreceptor can recognize an organic molecule in a stereospecific manner.

Because R-fendiline is a structurally simple molecule with selective andpotent effects on the parathyroid cell calcium receptor,structure-activity studies around this lead molecule are simple. The aimof these studies is to generate an array of related molecules withvarious characteristics from which the final development candidate canbe selected. This effort has already revealed some of the structuraldomains of R-fendiline that contribute to activity and potency. Forexample, the novel compound 1D is an analog of R-fendiline that issmaller (MW<240), yet nearly as potent as the parent molecule, whereasseveral other analogues are relatively inactive. The most interestingmolecules from this analog project can be put into in vivo testing foreffects on PTH secretion and serum Ca²⁺ levels (see Examples 15, 16, 17,18 and 23).

meta-Methoxyfendiline is another compound as potent as NPS 467 incausing the mobilization of intracellular Ca²⁺ in parathyroid cells.meta-Methoxyfendiline is a racemic mixture and it is anticipated thatthe resolution of meta-methoxyfendiline into its enantiomers will resultin an isomer that is more potent than the racemic mixture.

The novel compound NPS 467 is an even smaller molecule than R-fendiline,yet the former is about 3-fold more potent than the latter in causingincreases in Ca²⁺ !_(i) in parathyroid cells. Like fendiline, NPS 467 isa racemic mixture. Resolution of NPS 467 into its enantiomers providesan isomer of even greater potency than the racemic mixture, i.e., NPSR-467 (see Example 17).

Further structure-activity studies on molecules related to R-fendiline,NPS 467, meta-methoxyfendiline and NPS 568 yielded pure isomers withgreater potency than these molecules in their racemic forms. Forexample, the greater potency of NPS R-568 compared to NPS S-568 is shownin FIG. 28b using different cells lines transfected with nucleic acidencoding a human parathyroid calcium receptor (pHuPCaR4.0)

Results obtained with fendiline (NPS 456, FIG. 33) show that it elicitsoscillatory increases in Cl⁻ current at concentrations of 100 μM. Theresults obtained in this expression system with neomycin and fendilinedemonstrate that these molecules act directly on the calcium receptorbut not on control cells. NPS R-568 has subsequently been shown to bethe most potent molecule active on Xenopus oocytes expressing theparathyroid cell calcium receptor.

Results of testing some of the compounds shown in FIG. 36 are providedin Tables 7 and 8. The measured EC₅₀ values were determined by assayingfor increases in intracellular calcium using fura-2 loaded cells (seeExample 11 and Table 6).

                  TABLE 7                                                         ______________________________________                                        Examples of Arylalkylamine Compounds with In Vitro EC.sub.50                  Values Greater than 5 μM at the Parathyroid Cell Calcium                   Receptor                                                                      Compound Name or Code (from                                                   FIG. 36)            EC.sub.50 (μM)                                         ______________________________________                                        Fendiline (racemic) 15                                                        R-Fendiline         9                                                         S-Fendiline         >15                                                       NPS S-467           >30                                                       NPS S-568           30                                                        1A                  166                                                       1B                  776                                                       1C                  126                                                       1D                  48                                                        1E                  123                                                       1S                  128                                                       2A                  120                                                       7Y                  >30                                                       7Z(R-)              >30                                                       7Z(S-)              >100                                                      8Y                  >30                                                       20K                 >30                                                       20V                 >100                                                      ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        Arylalkylamine Calcimimetics from Figure 36 Active at the                     Parathyroid Cell Calcium Receptor In Vitro (EC.sub.50 ≦ 5 μM)       Compound Code          Compound Code                                          (from FIG. 36)                                                                            EC.sub.50 (μM)                                                                        (from FIG. 36)                                                                            EC.sub.50 (μM)                          ______________________________________                                        NPS R-467   2.0        11D         1.8                                        NPS R-568   0.60       11X         0.83                                       3U          0.64       11Y         2.8                                        3V          1.8        12L         1.7                                        4A          1.4        12U         1.2                                        4B          2.0        12V         0.42                                       4C          2.0        12W         3.2                                        4D          4.4        12Y         2.0                                        4G          1.8        13Q         ca. 0.8                                    4H          ≧3.0                                                                              13R         0.25                                       4J          2.2        13S         <0.13                                      4M          2.1        13U         0.19                                       4N          0.8        13X         <0.75                                      4P          1.6        14L         0.26                                       4R/6V       4.2        14Q         0.47                                       4S          3.3        14U         0.13                                       4T/4U       1.6        14V         1.7                                        4V          2.5        14Y         0.38                                       4W          2.3        15G         ca. 0.5                                    4Y          1.3        16Q         0.04                                       4Z/5A       4.4        16R         0.36                                       5B/5C       2.8        16T         0.04                                       5W/5Y       3.6        16V         <0.13                                      6E          2.7        16W         0.59                                       6F(R,R-)    0.83       16X         0.10                                       6R          3.4        17M         0.15                                       6T          2.9        17O         0.04                                       6X          2.5        17P         0.04                                       7W          3.2        17R         0.39                                       7X          1.1        17W         0.43                                       8D          2.5        17X         0.02                                       8J          0.78       20F         <1.0                                       8K          1.3        20I         >1.0                                       8R          2.6        20J         >3.0                                       8S          1.7        20R         2.4                                        8T          1.8        20S         4.2                                        8U          0.44       21D         3.0                                        8X          0.76       21F         0.38                                       8Z          0.40       21G         1.1                                        9C          0.60       21O         0.26                                       9D          1.4        21P         0.43                                       9R          0.25       21Q         1.4                                        9S          4.8        21R         0.37                                       10F         0.89                                                              ______________________________________                                    

Example 13 Osteoclast Calcium Receptor Lead Molecules

The strategy used for elucidating the mechanism of action ofextracellular Ca²⁺ on the osteoclast was similar to that proveneffective in parathyroid cells. The first experiments examined theeffects of La³⁺ on Ca²⁺ !_(i) in single rat osteoclasts loaded with thefluorimetric indicator indo-1. As described above, trivalent cationslike La³⁺ are impermeant and block Ca²⁺ influx. Low micromolarconcentrations of La³⁺ partially depressed extracellular Ca²⁺ -inducedincreases in Ca²⁺ !_(i) (FIG. 29). The demonstration of a La³⁺-resistant increase in Ca²⁺ !_(i) provides evidence for the mobilizationof intracellular Ca²⁺. The results of these experiments parallel thoseobtained in parathyroid cells and suggest that similar mechanisms areused by extracellular Ca²⁺ to regulate Ca²⁺ !_(i) in both cell types.

Another series of experiments showed that extracellular Mn²⁺ evokedtransient increases in Ca²⁺ !_(i) (FIG. 30(b)) that persisted in theabsence of extracellular Ca²⁺ (FIG. 30(a)). These results are likewiseindicative of the mobilization of intracellular Ca²⁺. Although Mn²⁺ canenter some cells, it is unlikely to do so in the osteoclast because Mn²⁺quenches the fluorescence of indo-1. Thus, if Mn²⁺ penetrated the cell,a decrease, not an increase in the fluorescent signal would be observed.

The results obtained with a variety of di- and trivalent cations are allconsistent with the presence of a calcium receptor on the surface of theosteoclast that is coupled to the mobilization of intracellular Ca²⁺ andinflux of extracellular Ca²⁺ through voltage-insensitive channels.Results show evidence for genetic material in human osteoclasts thatencodes a calcium receptor protein (see below). Transient increases inCa²⁺ !_(i) resulting from the mobilization of intracellular Ca²⁺, aresufficient to inhibit osteoclastic bone resorption in vitro. Thus, aswith the parathyroid cell, activation of the calcium receptor appears tobe a viable means of inhibiting the activity of osteoclasts.

Prenylamine was examined for its ability to inhibit bone resorption invitro. This was done by morphometric analysis of pit formation on thinslices of bovine cortical bone using scanning electron microscopy. Ratosteoclasts were incubated for 24 hours in slices of bone in thepresence or absence of various concentrations of prenylamine.Prenylamine caused a concentration-dependent inhibition of boneresorption with an IC₅₀ of 10 μM. The anticipated results provide thefirst demonstration that molecules acting at this novel site can inhibitosteoclastic bone resorption. More potent analogues of prenylamine willbe generated using synthetic chemistry and will be tested and assayedusing the methods described herein.

Example 14 C-Cell Calcium Receptor Lead Molecules

Activation of the C-cell calcium receptor stimulates the secretion ofcalcitonin which then acts on osteoclasts to inhibit bone resorption.Calcimimetic drugs selectively affecting C-cells are useful in thetreatment of osteoporosis.

The mobilization of intracellular Ca²⁺ is used as a functional index ofcalcium receptor activity. The screening effort in C-cells isfacilitated by the availability of cultured cell lines expressing theC-cell phenotype (e.g., rat medullary thyroid carcinoma cells; rMTC 6-23cells). Selected for initial study were three naturally occuringarylalkyl polyamines, agatoxin 489, agatoxin 505, and NPS 019. Agatoxin505 was found to block extracellular Ca²⁺ -induced increases in Ca²⁺!_(i) with an IC₅₀ of 3 μM. The inhibitory effect resulted from a blockof the L-type voltage-sensitive Ca²⁺ channel present in these cells. Incontrast, agatoxin 489 was found to mobilize intracellular Ca²⁺ in rMTCcells with an EC₅₀ of 150 μM. This was the first organic moleculediscovered that was found to activate the C-cell calcium receptor. NPS019 was even more potent and mobilized intracellular Ca²⁺ with an EC₅₀of 5 μM (FIG. 32).

It is significant that the only structural difference between NPS 019and agatoxin 489 is the presence or absence of an hydroxyl group. Thefact that such subtle differences in structure affect profoundly thepotency of molecules indicates a structurally specific binding site onthe calcium receptor. This, in turn, encourages the view that verypotent and selective activators of calcium receptors can be developed.

NPS 019, which is a small molecule (MW<500), is a lead molecule the fordevelopment of calcimimetics of the C-cell calcium receptor and can betested for its ability to stimulate calcitonin secretion in vitro.Subsequent in vivo testing will then determine the ability of thismolecule to stimulate calcitonin secretion and inhibit bone resorption.These in vivo studies will be performed in rats. The results obtained inthese studies, which are anticipated to be positive, will provide thefirst evidence showing that a small organic molecule acting on a novelreceptor can stimulate calcitonin secretion and depress bone resorption.

Example 15 Calcilytic Activity of NPS 021 on Parathyroid Cells

For a compound to be considered a calcilytic, it must block the effectsof extracellular Ca²⁺ or a calcimimetic compound on an extracellularCa²⁺ -sensing cell. An example of a calcilytic compound is NPS 021, thestructure of which is provided in FIG. 1a. In bovine parathyroid cellsloaded with fura-2, NPS 021 blocks increases in Ca²⁺ !_(i) elicited byextracellular Ca²⁺. The IC₅₀ of NPS 021 for blocking this response isabout 200 μM and, at concentrations around 500 μM, the increase in Ca²⁺!_(i) evoked by extracellular Ca²⁺ is abolished. Significantly, NPS 021does not by itself cause any change in Ca²⁺ !_(i) when tested at lowCa²⁺ ! (0.5 mM; FIG. 37). Ga³⁺ is also calcilytic to Xenopus oocytesexpressing the cloned calcium receptor: Ga³⁺ by itself has no effect onthe Cl⁻ currents activated by Gd³⁺, a calcimimetic, but pretreatmentwith Ga³⁺ blocks the action of Gd³⁺.

Example 16 NPS 467 Lowers Serum Ionized Calcium

Compounds shown to activate the bovine parathyroid cell calcium receptorin vitro were tested for hypocalcemic activity in vivo. MaleSprague-Dawley rats (200 g) were maintained on a low calcium diet forone week prior to receiving test substance or vehicle as control. Bloodwas collected from the tail vein three hours after the intra-peritonealadministration of NPS 467. Ionized Ca²⁺ in whole blood or serum wasmeasured with a Ciba-Corning 634 Analyzer according to the instructionsprovided with the instrument. Serum total calcium, albumin and phosphatewere measured by techniques well known in the art.

NPS 467 caused a dose-dependent reduction in serum or whole blood Ca²⁺(FIG. 38). The fall in blood Ca²⁺ at this time was paralleled by aproportional fall in the levels of blood total calcium. There was nochange in serum albumin or phosphate levels at any of the dosesexamined. In preliminary studies, NPS 467, at doses effective inlowering blood Ca²⁺, caused a dose-dependent reduction in circulatinglevels of PTH (FIG. 39). The hypocalcemic effect of NPS 467 was maximalwithin three hours and returned toward control levels after 24 hours(FIG. 40).

NPS R-467 (see Example 17) was also effective in lowering serum ionizedCa²⁺ in rats maintained on a normal, calcium-replete diet. A single doseof NPS R-467 (10 mg/kg i.p.) caused a rapid fall in serum levels ofionized Ca²⁺ which were maximal by 1 hour (22% decrease from the controllevel) and remained depressed at or near this level for up to 6 hours.

Example 17 NPS 467 Lowers Serum Ionized Calcium in a StereospecificManner

NPS 467 is a racemic mixture. Resolution of NPS 467 into its twoenantiomers was achieved by means of chiral HPLC. The R-isomer was about100-fold more potent than the S-isomer in activating the bovineparathyroid cell calcium receptor in vitro as assessed by the ability ofthe enantiomers to evoke increases in Ca²⁺ !_(i) in parathyroid cells(FIG. 41). Likewise, similar resolution of the novel compound NPS 568into its enantiomers showed that the R-isomer was 40-fold more potentthan the S-isomer in causing the mobilization of intracellular Ca²⁺ inbovine parathyroid cells (see Table 6, supra).

The isomers of NPS 467 were examined for effects on serum Ca²⁺ as inExample 16. Consistent with the in vitro results, the R-isomer of NPS467 proved to be more potent than the S-isomer in lowering serum Ca²⁺ invivo (FIG. 42; each compound was tested at a concentration of 5 mg/kgbody weight).

Example 18 NPS R-467 Lowers Serum Ionized Calcium in an In Vivo Model ofSecondary Hyperparathyroidism

An accepted and widely used animal model of secondaryhyperparathyroidism arising from chronic renal failure is the 5/6nephrectomized rat. Animals receiving such surgery become initiallyhypocalcemic and, to maintain serum. Ca²⁺ levels, there is acompensatory hyperplasia of the parathyroid glands and elevated levelsof circulating PTH. Male Sprague-Dawley rats (250 g) received a 5/6nephrectomy and were allowed to recover for 2 weeks. At this time theywere normocalcemic (due to elevated levels of serum PTH). Theadministration of NPS R-467 (10 mg/kg i.p.) caused a rapid (within 2hours) fall in serum ionized Ca²⁺ levels to 83% of controls in an animalmodel of secondary hyperparathyroidism. This suggests that compounds ofthis sort will effectively depress PTH secretion in patients withsecondary hyperparathyroidism and hyperplastic parathyroid glands.

Example 19 NPS R-467 Fails to Lower Serum Ionized Calcium Levels inParathyroidectomized Animals

To determine the primary target tissue upon which NPS R-467 acts tocause a hypocalcemic response, the parathyroid glands in rats weresurgically removed. Animals receiving a total parathyroidectomy becomehypocalcemic and are largely dependent upon dietary calcium to maintainserum Ca²⁺ homeostasis. Parathyroidectomized animals had serum ionizedCa²⁺ levels of 0.92 mM which fell gradually to 0.76 mM after 6 hours offasting. The administration of a single dose of NPS R-467 (10 mg/kgi.p.) did not cause any change in serum ionized Ca²⁺ levels over aperiod of 6 hours. These results demonstrate that intact parathyroidglands are required for the hypocalcemic effects of NPS R-467. The dataadditionally demonstrate that NPS R-467 can target the parathyroidglands in vivo. The results are consistent with the view that NPS R-467acts on the parathyroid cell calcium receptor in vivo to depresssecretion of PTH and thereby cause serum levels of ionized Ca²⁺ to fall.

Example 20 NPS R-467 and NPS S-467 Increase Intracellular Calcium inHuman Parathyroid Glands

Dissociated parathyroid cells were prepared from a parathyroid adenomaobtained by surgery from a patient with primary hyperparathyroidism. Thecells were loaded with fura-2 and Ca²⁺ !_(i) measured as describedabove. Both NPS R-467 and NPS R-568 caused concentration-dependentincreases in Ca²⁺ !_(i). The EC₅₀ 's for NPS R-467 and NPS R-568 were 20and 3 μM, respectively. Both of these compounds are thus able toincrease Ca²⁺ !_(i) in pathological human tissue and would thus beexpected to decrease serum levels of PTH and Ca²⁺ in patients withprimary hyperparathyroidism.

Example 21 Mechanism of Action of NPS R-467 at the Parathyroid CellCalcium Receptor

Dissociated bovine parathyroid cells were used to further explore themechanism of action of NPS R-467 at the receptor level. In the presenceof 0.5 mM extracellular Ca²⁺, NPS R-467 caused a rapid and transientincrease in Ca²⁺ !_(i) which persisted in the presence of 1 μM La³⁺ andwas partially depressed by pretreatment with PMA (100 nM for 2 minutes).Moreover, 30 μM of NPS R-467 caused a rapid increase in Cl⁻ current inXenopus oocytes injected with parathyroid cell mRNA. These results areconsistent with an action of NPS R-467 on the calcium receptor. However,the cytosolic Ca²⁺ response to NPS R-467 was abolished when parathyroidcells were suspended in Ca²⁺ -free buffer. This suggests that NPS R-467cannot, by itself, cause the mobilization of intracellular Ca²⁺. Itdoes, however, elicit responses in parathyroid cells and in oocytes whena small amount of extracellular Ca²⁺ is present. This suggests thatpartial occupancy of the Ca²⁺ -binding site is required for NPS R-467 toelicit a response.

To test this hypothesis, parathyroid cells were suspended in Ca²⁺ -freebuffer and exposed to a submaximal concentration of neomycin. Neomycinwas used because it mimics, in nearly all respects, the effects ofextracellular Ca²⁺ on parathyroid cells and on Xenopus oocytesexpressing the parathyroid cell calcium receptor. The addition of 10 μMneomycin did not by itself cause an increase in Ca²⁺ !_(i) under theseconditions. However, the subsequent addition of NPS R-467 (30 μM) nowelicited a transient increase in Ca²⁺ !_(i) which, because there was noextracellular Ca²⁺ present, must have come from the mobilization ofintracellular Ca²⁺.

When cells bathed in Ca²⁺ -free buffer were exposed to 30 μM NPS R-467,there was no increase in Ca²⁺ !_(i). This concentration of NPS R-467 ismaximally effective in increasing Ca²⁺ !_(i) when extracellular Ca²⁺(0.5mM) is present. However, the subsequent addition of 10 μM neomycinnow evoked a transient increase in Ca²⁺ !_(i). Presumably, neomycinbinds to the same site as extracellular Ca²⁺ and can functionallysubstitute for it. Using a submaximal concentration, which by itselfcauses no response, achieves partial occupancy of the Ca²⁺ -binding siteand allows activation of the calcium receptor by NPS R-467.

Additional studies to further define the mechanism of action of NPSR-467 were performed. The cells were once again suspended in Ca²⁺ -freebuffer to insure that any observed increase in Ca²⁺ !_(i) resulted fromthe mobilization of intracellular Ca²⁺. In these experiments, however, amaximally effective concentration (100 μM) of neomycin was used. In theabsence of extracellular Ca²⁺, 100 μM neomycin evoked a rapid andtransient increase in Ca²⁺ !_(i). The subsequent addition of 30 μM NPSR-467 did not cause an increase in Ca²⁺ !_(i).

In the converse experiment, 30 μM NPS R-467 was added before 100 μMneomycin. As expected, NPS R-467 did not cause any increase in Ca²⁺!_(i). It did not, however, affect the increase in Ca²⁺ !_(i) evoked bythe subsequent addition of 100 μM neomycin. These results, obtained withmaximally effective concentrations of NPS R-467 and neomycin, suggestthat these two compounds do not act at the same site. Rather, theresults can be sufficiently explained by postulating two separate siteson the calcium receptor, one to which extracellular Ca²⁺ and neomycinbind, and another to which NPS R-467 and structurally related compounds(such as NPS R-568) bind.

Ligand binding to the former site can result in full activation of thecalcium receptor whereas ligand binding to the latter site can onlyoccur and/or be functionally relevant when the extracellular Ca²⁺-binding site is occupied to some as yet undefined degree. It ispossible that ligand binding to the extracellular Ca²⁺ -binding siteexposes a previously occluded binding site for NPS R-467. It appearsthat the NPS R-467-binding site is an allosteric site that augmentsreceptor activation in response to ligand binding at the extracellularCa²⁺ binding site.

The data demonstrate that the parathyroid cell calcium receptorpossesses at least two distinct sites for organic ligands. One sitebinds the physiological ligand, extracellular Ca²⁺, and certain organicpolycations like neomycin. Binding to this site results in fullactivation of the calcium receptor, an increase in Ca²⁺ !_(i), and theinhibition of PTH secretion. NPS R-467 and NPS R-568 define a previouslyunrecognized binding site on the calcium receptor. Binding to this sitecan only occur and/or results in full activation of the calcium receptorwhen the extracellular Ca²⁺ -binding site is partially occupied. Ligandsacting at either site are effective in suppressing serum Ca²⁺ levels invivo.

Allosteric Site on Parathyroid Cell Calcium Receptor

Calcimimetic compounds that activate the bovine parathyroid cell calciumreceptor, such as NPS R-467 and NPS R-568, do not cause the mobilizationof intracellular Ca²⁺ in the absence of extracellular Ca²⁺. Rather, theyincrease the sensitivity of the calcium receptor to activation byextracellular Ca²⁺, thus causing a shift to the left in theconcentration-response curve for extracellular Ca²⁺. Because of this, itis unlikely that they act at the same site on the receptor as doesextracellular Ca²⁺. In contrast, organic and inorganic polycations docause the mobilization of intracellular Ca²⁺ in the absence ofextracellular Ca²⁺ and therefore probably act at the same site as doesextracellular Ca²⁺. Compounds like NPS R-568, presumably act in anallosteric manner and their activity is dependent on some minimal levelof extracellular Ca²⁺. This suggests that partial occupancy of theextracellular Ca²⁺ -binding site on the receptor is required forcompounds like NPS R-568 to be effective. This model is consistent withthe observations described in Example 21.

Other details of the mechanism of action of NPS R-568 on the parathyroidcell calcium receptor, however, are more accurately investigated bybinding studies in which the specific binding of radiolabeled (using ³ Hfor example) NPS R-568 is assessed. There are several molecularmechanisms that could explain the activity of NPS R-568 on theparathyroid cell calcium receptor. In one mechanism (model 1), NPS R-568could bind to the calcium receptor at a site that, when occupied, is notsufficient to activate the receptor functionally. Activation only occurswhen some level of occupancy of the extracellular Ca²⁺ -binding site(s)is achieved. In an alterative mechanism (model 2), the occupation of theextracellular Ca²⁺ -binding site could unmask latent binding sites forcompounds such as NPS R-568. Occupancy of this latent site by NPS R-568then increases affinity and/or efficacy of binding at the extracellularCa²⁺ site. Either mechanism involves a form of allosteric activation ofthe calcium receptor by compounds such as NPS R-568. These are not theonly possible mechanisms that could explain the effect of compounds likeNPS R-568 on the parathyroid cell calcium receptor. Other mechanisms ofaction may be suggested by the results of the binding studies describedbelow.

To further investigate the mechanism of action of compounds like NPSR-568 on the parathyroid cell calcium receptor, binding studies using ³H-NPS R-568 can be performed. The specific binding of ³ H-NPS R-568 tointact parathyroid cells or to membranes prepared from parathyroid cellsis initially investigated by techniques well known in the art. Thekinetic parameters of binding will then be measured as a function ofextracellular Ca²⁺ concentrations. Specifically, Scatchard analysis ofthe data will reveal the number of binding sites and the apparentaffinity of the receptor site for ³ H-NPS R-568. These parameters willthen be investigated as a function of changes in the level ofextracellular Ca²⁺ in the buffer used for the assay. If model 1 iscorrect, then a significant level of specific binding should occur inthe absence of extracellular Ca²⁺. Large changes in the kineticparameters of binding as a function of the level of extracellular Ca²⁺would favor model 2. It is expected that various other inorganic andorganic polycations described above in other examples will cause similarchanges in the binding parameters of ³ H-NPS R-568 as does extracellularCa²⁺. This would support the view that these polycations act at theextracellular Ca²⁺ -binding site, which is distinct from that to whichcompounds like NPS R-568 bind.

Example 22 Synthesis and Chiral Resolution of NPS 467

This example describes a protocol used to synthesis NPS 467 and itsresolution into individual enantiomers. In a 250-ml round-bottom flask,10.0 g (100 mmoles) 3'-methoxyacetophenone and 13.5 g (100 mmoles)3-phenylpropylamine were mixed and treated with 125 mmoles (35.5 g)titanium(IV) isopropoxide. The reaction mixture was stirred 30 minutesat room temperature under a nitrogen atmosphere. After this time 6.3 g(100 mmoles) sodium cyanoborohydride in 100 ml ethanol was addeddropwise over the course of 2 minutes. The reaction was stirred at roomtemperature under nitrogen for 16 hours. After this time the reactionmixture was transferred to a 2-L separatory funnel with 1.5 L of diethylether and 0.5 L of water. The phases were equilibrated and the etherlayer removed. The remaining aqueous phase was thoroughly extracted withfour 1-L portions of diethylether. The washes were combined, dried overanhydrous potassium carbonate and reduced to a clear, light amber oil.

TLC analysis of this material on silica gel usingchloroform-methanol-isopropylamine (100:5:1) showed product at R_(f)0.65 with traces of the two starting materials at R_(f) 0.99 (3'-methoxyacetophenone) and R_(f) 0.0 (3-phenylpropylamine).

The reaction mixture was chromatographed through silica gel (48×4.6 cm)using a gradient of chloroform-methanol-isopropylamine (99:1:0.1) to(90:10:0.1) which yielded 13.66 g of purified NPS 467. This material wasdissolved in hexane-isopropanol (99:1) containing 0.1% diethylamine toyield a solution with a concentration of 50 mg/ml. Chiral resolution wasaccomplished by chromatography of 4 ml of this solution (200 mg, maximumto achieve separation) through ChiralCel OD (25×2 cm) using 0.7%isopropanol, 0.07% diethylamine in hexane at 10 ml/min, monitoringoptical density at 260 nm.

Under these conditions (with injections of 100 mg material) theearly-eluting isomer (NPS R-467;(R)-(+)-N-(3-phenylpropyl)-α-methyl-3-methoxybenzylamine) began toemerge from the column at about 26 minutes, the late-eluting isomer (NPSS-467) began to emerge at about 34 minutes. Baseline resolution wasaccomplished under these conditions. Each optical isomer (free base) wasconverted to the corresponding hydrochloride salt by dissolving 3 g ofthe free base in 100 ml ethanol and treating it with 100 ml watercontaining 10 molar equivalents HCl. Lyophilization of these solutionsyielded white solids.

Example 22 Synthesis of NPS R-568

NPS R-568, (R)-(+)-N-3-(2-chlorophenyl)propyl!-α-methyl-3-methoxybenzylamine, was synthesizedusing the methods described in Example 22 substituting an equivalentamount of 3-(2-chlorophenyl)propylamine for 3-phenylpropylamine. It wasfound that allowing the mixture of 3'-methoxyacetophenone,3-(2-chlorophenyl)propylamine and titanium(IV) isopropoxide to stir for5 hours prior to treatment with NaCNBH₃ /EtOH resulted in significantlygreater yield (98%).

Example 24 NPS R-467 Lowers Serum Ionized Calcium when AdministeredOrally

Rats (male, Sprague-Dawley, 250-300 g) were fed standard rat chow andfasted overnight prior to the experiment. NPS R-467 was suspended incorn oil and administered as a single oral dose through a gavage needle.Three hours later a sample of blood was taken from the tail vein andassessed for ionized Ca²⁺ levels. FIG. 44 shows that NPS R-467 caused adose-dependent reduction in serum levels of ionized Ca²⁺ whenadministered orally.

Example 25 BoPCaR 1 Cloning Method

This example describes the cloning of a bovine parathyroid calciumreceptor using an expression cloning strategy. The expression cloningstrategy involved assaying the ability of nucleic acid to express apolypeptide which activates Cl⁻ currents in Xenopus laevis oocytes. X.laevis oocytes were chosen as hosts, to express nucleic acid encodingthe bovine parathyroid calcium receptor, based on the following factors:(i) they exhibit a high level of maturity (i.e., Stage V, VI); (ii) theyexhibit a high activity of Cl⁻ currents activated by Ca²⁺ ionophoreslike A23187; (iii) they exhibit a high level of functional expression ofGd³⁺ -induced Cl⁻ current when injected with 25 ng/oocyte of totalpoly(A)⁺ -mRNA isolated from bovine parathyroid.

The techniques used to clone the parathyroid calcium receptor arebriefly described in this example; a more complete description of thetechniques is provided in preceding sections, which describe techniqueswhich may be used to clone additional forms of the Ca²⁺ -receptor fromother cell types. Poly(A⁺)-enriched mRNA was initially prepared frombovine parathyroid glands by extracting with guanidinium thiocyanate,centrifugation through CsCl and oligo (dT) cellulose chromatography.Injection of the resultant poly(A⁺)-enriched mRNA into oocytes (25-50ng/oocyte ) conferred sensitivity to elevated extracellularconcentrations of Ca²⁺ and the trivalent cation (1-100 μM) Gd³⁺ asdescribed herein, such that the two cations elicited calcium-activatedchloride currents. No such currents were elicited in control eggsinjected with water.

The mRNA was then subjected to size fractionation, utilizingpreparative, continuous flow agarose gel electrophoresis (Hediger, M.A., Anal. Biochem. 159:280-286 (1986)) to obtain fractions ofpoly(A⁺)-mRNA further enriched in transcripts coding for the Ca²⁺receptor. Oocytes injected with size-fractionated mRNA of about 4-5.5 Kbshowed enhanced expression of Gd³⁺ -activated Cl⁻ currents.

Size-fractionated mRNA of about 4-5.5 Kb in size were used to prepare asize-selected, directional cDNA library in the plasmid pSPORT1 that wasenriched in full-length transcripts. Sense complementary RNA (cRNA) wasthen synthesized from the DNA inserts pooled from 350-500 independentclones from this library and injected into oocytes. Gd³⁺ -activated Cl⁻currents were observed following injection of RNA from a single filtercontaining 350 colonies. Preparation and injection of cRNA fromsuccessively smaller pools of clones led to isolation of a single clone(BoPCaR 1) with a cDNA insert of 5.3 kb which expressed greatly enhancedCa²⁺ -receptor activity following injection of its cRNA into oocytes. Aplasmid containing the BoPCaR 1 cDNA (See restriction map, FIG. 45;plasmid, FIG. 46; and nucleotide sequence (SEQ. ID. NO. 1), FIG. 47) hasbeen deposited in the ATCC under deposit number 75416.

The BoPCaR 1 cDNA is outside the size range of the size-selected RNAfound to express neomycin elicited Cl⁻ channel activity in Xenopusoocytes. This is consistent with the possibilities that differentisoforms of the calcium receptor exist or that multiple genes encodeother members of the calcium receptor gene family.

Several pharmacological and biochemical criteria were used to identifythis clone as encoding a bona fide bovine parathyroid Ca²⁺ receptor.Oocytes expressing the cloned receptor, but not water-injected oocytes,responded to increasing concentrations of extracellular Ca²⁺ (1.5-5 mM)or Gd³⁺ (20-600 μM) with large increases in Cl⁻ currents (up to at least1.8 microamperes) that were several-fold larger than those observed inpoly(A⁺)-injected oocytes. These responses increased markedly over aperiod of one to four days after injection of the eggs with cRNAprepared from the BoPCaR 1 cDNA. Furthermore, the ranges of theconcentrations of the two cations eliciting this response were verysimilar to those shown previously to act on bovine parathyroid cells invitro. Neomycin (20-100 μM), which is known to closely mimic the effectsof Ca²⁺ on parathyroid cells, produced changes in Cl⁻ current in oocytesessentially identical to those produced by Ca²⁺ or Gd³⁺, and theseoccurred over the same range of concentrations over which thisantibiotic modulates parathyroid function in vitro.

Finally, in vitro translation of RNA prepared from the clone resulted ina single major protein on polyacrylamide gels with a molecular weight ofabout 120 kd, whose synthesis was enhanced by inclusion of dogpancreatic microsomes, concomitant with an increase in apparentmolecular weight of 10-15%. The latter suggests that the cloned receptorinteracts strongly with membranes, as might be expected of an integralmembrane protein receptor, and is glycosylated in its native form.Studies with the lectin concanavalin A indicate that the Ca²⁺ receptoris likely a glycoprotein. Thus, the pharmacological properties of thecloned receptor, which is expressed at high levels in oocytes, as wellas the biochemical studies carried out to date are completely consistentwith its identity as the bovine parathyroid Ca²⁺ receptor.

Oocytes injected with cRNA (50 nl of 0.125 μg/ml) prepared from BoPCaR1show large inward currents in response to elevated extracellularconcentrations of Ca²⁺ (5 mM), Mg²⁺ (1.0-20 mM) , Gd³⁺ (600 μM) , orneomycin (200 μM) , resulting from activation of the Ca²⁺ -activatedchloride currents. These responses are mediated by the following seriesof biochemical events:

(1) Activation of phospholipase C by a pertussis toxin-sensitive guaninenucleotide regulatory (G) protein resulting in 4-7 fold increases in thelevels of inositol 1,4,5-triphosphate (IP₃). Preincubation with 10 μg/mlof pertussis toxin for 48 hours inhibits the increase by 75%;

(2) Release of Ca²⁺ from intracellular stores. The several-fold increasein the Ca²⁺ !_(i) measured in oocytes loaded with the Ca²⁺ -sensitivefluorescent dye, fluo-3, persists even when the oocytes are exposed toGd³⁺ or neomycin in the absence of extracellular Ca²⁺. Furthermore, theinward currents elicited by Gd³⁺ or neomycin also persist despiteremoval of extracellular Ca²⁺.

(3) The polyvalent cation-induced increases in Ca²⁺ !_(i) are necessaryfor the associated electrophysiological responses. The Ca²⁺ chelator,EGTA (100 μM), prevents oocytes expressing the calcium receptor fromresponding with inward currents to 600 μM Gd³⁺.

(4) The activated currents appear to be Ca²⁺ -activated chloridecurrents. The currents are activated by the divalent cation ionophore,A23187, which raises Ca²⁺ !_(i). The chloride channel-blocker 9AC blocksthe currents.

Example 26 Use of NPS R-568, and Other Compounds, as a Diagnostic Tool

NPS R-568 or other compounds active on a calcium receptor can be used asa diagnostic tool. Specifically, a pharmaceutical preparation of suchcompounds is useful as a diagnostic tool. In one example, apharmaceutical preparation containing a parathyroid cell calcimimeticcompound such as NPS R-568 can be given by oral or another route ofadministration to hypercalcemic patients with symptoms of mentaldepression. If these symptoms arise from an underlying hyperparathyroidstate, such as primary hyperparathyroidism, then administration of NPSR-568 or a compound that acts similarly will alleviate those symptoms.If the symptoms do not abate, then the mental depression results fromsome pathological state that is not hyperparathyroidism. Thus,parathyroid cell calcimimetic compounds can be used in the differentialdiagnosis of mental depression.

Symptoms and signs common to hyperparathyroidism and other disorders canalso be differentially diagnosed in the manner described above. Suchshared signs and symptoms include, but are not limited to, hypertension,muscular weakness, and a general feeling of malaise. Alleviation ofthese symptoms following treatment with a parathyroid cell calciumreceptor calcimimetic compound would indicate that the problems resultfrom the underlying hyperparathyroidism.

In another example, a compound acting as an antagonist (calcilytic) atthe C-cell calcium receptor can be administered as described above todiagnose medullary thyroid carcinoma. In this case, administration ofthe C-cell calcium receptor calcilytic compound will depress serumlevels of calcitonin which can be readily measured by radioimmunoassay.Certain symptoms associated with medullary thyroid carcinoma, such asdiarrhea, may also be monitored to determine if they are abated orlessened following administration of the calcilytic compound.

In a third example, a compound acting as a calcimimetic at thejuxtaglomerular cell calcium receptor can be used in the differentialdiagnosis of hypertension. In this case, administration of thejuxtaglomerular cell calcium receptor calcimimetic compound can becarried out as described above. A decrease in blood pressure to normallevels will occur if the hypertension results mostly or exclusively fromelevated levels of renin rather than from an alternative pathologicalstate.

In another example, a compound acting as a specific calcimimetic on theosteoclast calcium receptor can be used in the differential diagnosis ofhigh- and low-turnover forms of osteoporosis. In this case, such acompound can be administered in a suitable pharmaceutical preparationand the levels of serum alkaline phosphatase, osteocalcin, pyridinolineand/or deoxypyridinoline crosslinks, and/or some other predictive markerof bone resorption and/or formation measured by techniques well known inthe art. A large decrease in one or more of these parameters would bepredictive of high-turnover osteoporosis, whereas a small or no decreasein these parameters would be predictive of low-turnover osteoporosis.Such information would dictate the appropriate treatment. Antiresorptivedrugs would not be the appropriate sole therapy for low-turnoverosteoporosis.

These examples are not exhaustive but serve to illustrate that specificcalcium receptors can be targeted with pharmaceutical preparations andthat the observed effects of such preparations on bodily functionsand/or chemical constituents can be used diagnostically. In general,calcimimetic and calcilytic compounds that act on calcium receptors ofthe various cells described above can be used in the diagnosis of thevarious diseases associated with the particular cell type. Thesediseases include, but are not limited to, bone and mineral-relateddisorders (as described in Coe and Favus, Disorders of Bone and MineralMetabolism, Raven Press, 1990), kidney diseases, endocrine diseases,cancer, cardiovascular diseases, neurological diseases, gastrointestinaldiseases, and diseases associated with gestation. Examples of humandiseases or disorders in which such molecules may be therapeuticallyeffective are as follows:

(1) A calcimimetic is expected to ameliorate psoriasis by reducing theproliferation of the abnormal skin cells.

(2) Since Ca²⁺ blocks the effect of vasopressin on MTAL and corticalcollecting duck cells, a calcimimetic is expected to reduce waterretention in states of vasopressin excess, such as the syndrome ofinappropriate vasopressin (ADH) secretion. Conversely, calcium receptorantagonists used in states of ADH deficiency are expected to potentiatethe action of any ADH present, such as in partial central diabetesinsipidus.

(3) Calcimimetics may be used to treat hypertension by: (a) reducingrenin secretion and/or (b) by stimulating production of vasodilatorssuch as PTHrP (PTH-related peptide) by vascular smooth muscle.

(4) Calcimimetics are expected to increase platelet aggregability, whichmay be useful when platelet counts are low. Conversely, calcilytics areexpected to inhibit platelet function in states where there ishypercoagulability.

(5) Calcium promotes differentiation of colon and mammary cells. Acalcimimetic is expected to reduce the risk of colon or breast cancer.

(6) Calcium promotes urinary calcium excretion in the MTAL. Acalcimimetic is expected to have a useful hypocalcemic action in thetherapy of hypercalcemic disorders. The inhibitory effect ofcalcimimetics on osteoclasts and their stimulation of the secretion ofthe hypocalcemic peptide calcitonin make them expected to be useful inthe therapy of hypercalcemia and its symptoms. A calcimimetic may alsoimprove hypocalcemic symptoms by activating calcium receptors.Conversely, a calcilytic is expected to reduce urinary calcium excretionand be useful in the treatment of kidney stones. In addition, Calciumsuppresses the formation of 1,25-dihydroxyvitamin D in the proximalrenal tubule, and this vitamin D metabolite is frequently overproducedin renal stone patients and contributes to their hypercalciuria.Suppression of 1,25-dihydroxyvitamin D formation by a calcimimetic isexpected to be useful in treating renal calcium stone disease.

(7) Endogenous amines could reproduce the symptoms in uremic patients bycalcimimetic or calcilytic actions. Calcimimetic and/or calcilyticagents are expected to improve these symptoms.

(8) Some of the renal toxicity of aminoglycoside antibiotics may bemediated by interaction of these drugs with renal calcium receptors.Having the calcium receptor is expected to make it possible to carry outdrug screening easily when designing new drugs of these classes tominimize renal toxicity. In addition, a renal calcium receptorantagonist would prevent or treat this renal toxicity if it is relatedto this mechanism.

(9) Some of the genetic component of calcium-related disorders, such asosteoporosis, renal stones, and hypertension are expected to be relatedto inherited problems with certain forms of the receptor. These now canbe studied and genetic screening/testing carried out usingreceptor-based reagents. The human disease, familial hypocalciurichypercalcemia, may be due to a calcium receptor defect. Definitivediagnostic separation from cases of primary hyperparathyroidism could becarried out with receptor-based technology.

(10) Calcium receptors are present in the placenta and are expected toimpact on disorders of placental function and transfer of nutrients tothe growing fetus.

Example 27 Cloning of Human Parathyroid Calcium Receptor from a HumanParathyroid Gland Adenoma Tumor

This example describes the cloning of a human parathyroid calciumreceptor from a human parathyroid gland adenoma tumor using pBoPCaR1 asa hybridization probe. The probe was used to identify nucleic acidencoding human parathyroid gland calcium receptor by cross-hybridizationat reduced stringency.

Messenger RNA was prepared from a human parathyroid gland adenoma tumorremoved from a 39-year-old Caucasian male diagnosed with primaryhyperparathyroidism. Northern blot analysis of this mRNA using pBoPCaR1as a hybridization probe identified calcium receptor transcripts ofabout 5 Kb and about 4 Kb. A cDNA library was constructed from the mRNA.Double-stranded cDNA larger than 3 Kbp were size-selected on an agarosegel and ligated into the cloning vector lambda ZapII. Five hundredthousand primary recombinant phage were screened with the 5.2 Kbp cDNAinsert of pBoPCaR1 as a hybridization probe. The. pBoPCaR1 insert waslabeled by random-primed synthesis using ³² P!-dCTP to a specificactivity of 1×10⁹ cpm/μg.

Library screening was performed at a hybridization stringency of 400 mMNa⁺, 50% formamide at a temperature of 38° C. Plaque lift filters werehybridized at a probe concentration of 500,000 cpm/ml for 20 hours.Following hybridization, filters were washed in 1×SSC at 40° C. for 1hr.

The primary screen identified about 250 positive clones identified byhybridization to pBoPCaR1. Seven of these clones were taken throughsecondary and tertiary screens to isolate single clones that hybridizedto the pBoPCaR1 probe. These seven clones were analyzed by restrictionenzyme mapping and Southern blot analysis. Three of the clones containedcDNA inserts of about 5 Kbp and appear to be full-length clonescorresponding to the 5 Kb mRNA. Two of the clones contain cDNA insertsof about 4 Kbp and appear to be full-length clones corresponding to the4 Kb mRNA.

Restriction enzyme mapping of the two different sized inserts indicatethat they share regions of sequence similarity in their 5' ends, butdiverge in their 3' end sequences. DNA sequence analyses indicate thatthe smaller insert may result from alternative polyadenylation upstreamof the polyadenylation site used in the larger insert.

Representative cDNA inserts for both size classes were subcloned intothe plasmid vector pBluescript SK. Linearization followed by in vitrotranscription using T7 RNA polymerase produced cRNA transcripts. ThecRNA transcripts were injected into Xenopus oocytes (150 ng/μl RNA; 50nl/oocyte) for functional analysis. Following incubation periods of 2-4days, the oocytes were assayed for the presence of functional calciumreceptors. Both clone types gave rise to functional calcium receptors asassessed by the stimulation of calcium-activated chloride currents uponaddition of appropriate calcium receptor agonists. Known calciumreceptor agonists, including NPS R-467 and NPS R-568, activated theoocyte-expressed receptor at about the same concentrations known to beeffective for the native parathyroid cell receptor. Thus, both clonesencode a functional, human parathyroid cell calcium receptor.

Plasmids were prepared by subcloning each size class of insert intopBluescript thereby producing pHuPCaR 5.2 and pHuCaR 4.0. The nucleicacid sequence, and amino acid sequence, of the inserts are shown inFIGS. 48 (pHuPCaR 5.2, SEQ. ID. NO. 2) and 49 (pHuPCaR 4.0, SEQ. ID. NO.3).

Several differences were observed between the nucleic acid sequences ofthe two cDNA inserts. Sequence analyses of the two cDNA inserts indicatethe existence of at least two sequence variants differing in the 3'untranslated region and which may result from alternativepolyadenylation (see SEQ. ID. NOs. 2 and 3). In addition, sequencevariation exists at the 5' end of the inserts (see SEQ. ID. NOs. 2 and3). These distinct sequences correspond-to untranslated regions and mayhave arisen due to alternative transcriptional initiation and/orsplicing.

Three additional sites of sequence variation are observed within thecoding regions of cDNA clones pHuPCaR4.0 and pHuPCaR5.2 (see SEQ. ID.NOs. 2 and 3) demonstrating that these cDNA clones encode distinctproteins. Sequence analysis of the human CaR gene (obtained fromoverlapping clones as described in Example 29) indicates that theadditional 30 base pairs of DNA in cDNA clone pHuPCaR5.2, as compared tothe pHuPCaR 4.0 cDNA clone, results from alternative mRNA splicing. Thealternative mRNA splicing is predicted to insert 10 additional aminoacids into the CaR polypeptide encoded by the pHuPCaR5.2 cDNA at a sitebetween aa#536 and aa#537 in polypeptide encoded by pHuPCaR4.0 cDNA. Inaddition, pHuPCaR4.0 encodes glutamine (Gln) at aa#925 and glycine (Gly)at position 990 whereas pHuPCaR5.2 encodes arg (Arg) at both equivalentpositions. The human CaR gene encodes for Gln and Arg, respectively, atthese positions. The difference between the pHuPCaR4.0 cDNA compared tohuman DNA appears to represent a true sequence polymorphism within thehuman population while the single base change in pHuPCaR5.2 probablyreflects a mutation which occurred during its cloning. Both cDNAs encodefunctional calcium receptors as demonstrated by the ability of Xenopusoocytes injected with cRNA prepared from these cDNA clones to respond to10 mM extracellular calcium as ascertained by Cl- conductance. However,it is possible that these two receptor isoforms are functionally and/orpharmacologically distinct.

Example 28 Cloning a Calcium Receptor from Normal Human ParathyroidTissue

This example describes the cloning of a calcium receptor from normalhuman parathyroid tissue. Experimental evidence has shown thatparathyroid cells from adenomatous tissue are less responsive toincreases in extracellular calcium (they have an elevated calcium"set-point"). It has been postulated that this change may arise from analteration of the calcium receptor itself. One of the uses of the clonedreceptor found in normal parathyroid tissue is to compare its primarynucleic acid sequence with that of the calcium receptor found inadenomatous tissue to determine if there are any differences in thenucleic acid sequences. Such differences may account for the alterationin the calcium receptor and may be used to further characterize regionsof the calcium receptor associated with responsiveness to calcium.

Parathyroid glands (150 mg) were removed at autopsy from a 69-year-oldCaucasian female with no history of parathyroid disease. Messenger RNAwas prepared from this tissue and used in the construction of a cDNAlibrary. cDNA inserts from this library were not size-selected.Six-hundred-thousand primary recombinants were screened with probe madefrom the 5.2 Kbp cDNA insert from the human calcium receptor clone,pHuPCaR-5.2. Hybridization was carried out at 42° C. and filters werewashed at a stringency of 1×SSC, at 52° C. The primary screen identifiedabout 30 positive clones, twelve of which were isolated andcharacterized. Partial sequence analysis indicated that these clones areessentially identical to cDNA sequences obtained from ademonousparathyroid (see Example 27).

Example 29 Isolation of Human Genomic Clones with Homology to theCalcium Receptor

Human calcium receptor genomic clones were isolated using the pBoPCaR1cDNA insert as a hybridization probe. In particular, a human genomic DNAlibrary, obtained from Stratagene, was screened using the pBoPCaR1 cDNAinsert as hybridization probe.

A portion of the library (500,000 clones) was screened with the pBoPCaR1cDNA insert by hybridizing in 400 mM Na⁺, 50% formamide, at 37° C., andwashing with 1×SSC at 40° C. Twenty-four clones were identified. Thenucleic acid from these clones were analyzed by restriction mapping andSouthern blot analysis using distinct regions of the pHuPCaR-5.2 cDNAinsert as hybridization probes. Nine of the 13 clones encoded portionsof the human parathyroid calcium receptor gene as evinced byhybridization to pHuPCaR-5.2 cDNA. The complete gene is represented onoverlapping clones pHuCaR-#4, #5, #6, #7 and #9. DNA sequence analysisof these clones indicates that the receptor is encoded by seven codingexons. The majority of the receptor mRNA (3' end) appears to be encodedby a single exon. The receptor encoded by these genomic clones isessentially identical to those encoded by cDNA clones pHuPCaR4.0 andpHuPCaR5.2 (Seq. ID. Nos. 2 and 3) (see Example 27, supra, whichdescribes the differences between the human nucleic acid sequenceobtained from overlapping clones pHuCaR-#4, #5, #6, #7 and #9,pHuPCaR4.0 and pHuPCaR5.2). Equivalent clones can be isolated asdescribed herein, as can other clones encoding members of this receptorfamily.

EXAMPLE 30 Cloning Ion Receptors from the Kidney

This example describes the cloning of ion receptors from rat kidneycells using pBoPCaR1 as a hybridization probe. A cDNA library wasprepared from rat kidney outer medulla mRNA size-fractionated to containtranscripts between 3 and 7 Kb. About seventy-five-thousand clones werescreened using pBoPCaR1 as a hybridization probe at 42° C. overnightfollowed by washing in 0.5× SSCP at 42° C. Three positive clones wereidentified.

Clone 3A (pRakCaR 3A) contained an insert of about 4.0 Kbp. The nucleicacid and amino acid sequence of the 3A insert is shown in FIG. 50 (SEQ.ID. NO. 8). Northern, analysis indicated that pRakCaR 3A hybridized toboth 7.5 Kb and 4.0 Kb transcripts. DNA sequence analysis of clone 3A(SEQ. ID. No. 4) indicates that it is highly homologous to other calciumreceptor sequences. Xenopus oocyte analysis of in vitro transcripts ofthe clone confirmed that clone pRakCaR 3A encodes a functional calciumreceptor.

EXAMPLE 31 Cloning of C-cell Calcium Receptor

This example describes the cloning of human thyroid C-cell calciumreceptor using pHuPCaR 5.2 as a hybridization probe. Functional evidenceindicates that the calcitonin-secreting C-cells of the thyroid glandexpress a calcium receptor. Pharmacological evidence indicates that thisreceptor is functionally distinct from the parathyroid calcium receptor.Northern blot analysis of human, bovine and rat thyroid gland mRNAidentifies a faintly hybridizing transcript when pHuPCaR-5.2 is used ashybridization probe. The diminished intensity of the identifiedtranscript may be due either to low abundance (C-cells represent 0.01%to 1% of thyroid cells) or may indicate structural differences betweenparathyroid and C-cell calcium receptors.

Northern blot analysis of a rat C-cell line (44-2) using a rat calciumreceptor genomic clone as hybridization probe identifies a single,moderately abundant transcript about 8.0 Kb. This is similar to the sizeof the rat parathyroid calcium receptor transcript and provides evidencethat C-cells express a calcium receptor. DNA sequence analysis ofproducts from polymerase chain reaction amplification of selectedregions of the rat C-Cell calcium receptor showed it to be essentiallyidentical to the calcium receptor encoded by the rat kidney cDNA cloneof Example 31 (FIG. 50).

A human C-cell calcium receptor was cloned from a thyroid cDNA libraryobtained from Clonetech. The library was prepared from tissue obtainedat autopsy from normal Caucasian males (trauma victims; no history ofthyroid disease). About five-hundred-thousand recombinant phage werescreened at a stringency of 400 mM Na⁺, 50% formamide at a temperatureof 40° C., and filters were washed at 1× SSC, 42° C. Four cDNA cloneshybridizing with pHuPCaR-5.2 were obtained. Insert sizes ranged from 0.8to 2 Kbp. Initial sequence analysis indicates that this calcium receptorsequence is highly homologous to the human parathyroid calcium receptor.Equivalent clones can be readily isolated as described herein.

EXAMPLE 32 Cloning Inorganic ion Receptors by Use of Degenerate SequencePCR

Analysis of the calcium receptor sequences (bovine and human) bysequence database comparison indicates that the calcium receptorsequence is unique. No significant homology is obvious to any knownprotein or nucleic acid sequence with one exception. The parathyroidcalcium receptor exhibits weak, but significant homology (20-30% aminoacid identity) with the metabotropic glutamate receptors (mGluRs). Thissurprising and unexpected result indicates that calcium receptors arestructurally related to mGluRs and probably evolved from a commonancestral gene several hundred million years ago. However, calciumreceptors are functionally distinct from mGluRs and in experiments onbovine parathyroid cells, or on Xenopus oocytes ectopically expressingcalcium receptors, did not respond to the mGluR agonists glutamate,trans-ACPD and quisqualate.

The discovery of the calcium receptor sequence makes it possible todetermine regions of extremely high sequence conservation. Such regionsare useful for guiding the preparation of hybridization and PCR probeswhich can be used to detect and isolate cDNA and genomic sequencesencoding additional related receptors such as inorganic ion receptors.

Analysis of the amino acid sequences of calcium receptors and mGluRsindicates that the homology is highest in several limited regionsincluding portions of both N-terminal putative extracellular domains andthe seven-transmembrane domain regions. Based on the later, fourdegenerate oligonucleotides have been synthesized for use in PCR. Theseare:

    ______________________________________                                        TM2:                                                                          CCTGCTCGAGACIA(A,G)(C,T)CGGGA(A,G)CT(C,T)T(C,G)CTA                            (C,T)(C,A)T;                                                                  TM5:                                                                          CGGAATTCCGTTICGGG(A,T)(C,T)TTGAA(C,G)GC(A,G)(A,T)A                            (G,C);                                                                        CL1:                                                                          CCTGCTCGAGTCAAGGCTACG(A,G)(A,G)I(C,A)G(G,A,C,T)GA                             (G,A)(C,T)T;                                                                  and, CL3:                                                                     CGGAATTCCATTTGGCTTCGTTGAAI(T,G)T(A,G,C,T)(G,T)C                               (G,A,T,C)GG.                                                                  ______________________________________                                    

These oligonucleotides contain XhoI or EcoR1 restriction sites within"PCR anchors" at their 5' ends to facilitate subcloning of theamplification products. The sequences were selected based onconservation of sequences within transmembrane domains 2 and 5 andcytoplasmic loops 1 and 3.

Four different primer combinations can be used to obtain ion receptorclones: TM2+TM5, TM2+CL3, CL1+TM5, and CL1+CL3. PCR reactions werecarried out using standard conditions (see, e.g., Abe et al. J. Biol.Chem., 19: 13361 (1992)) using annealing temperatures between 37° C. and55° C. Each combination gave rise to products approximately 500 bp whenused to amplify cDNAs or genomic DNAs containing ion receptors and/ormGluRs. Libraries of such PCR products have been prepared afteramplification of such sequences from cDNAs prepared from a variety oftissues, and from genomic DNA. Analysis of the products resulted in thedetection of parathyroid calcium receptor sequences, 5 mGluR sequencesand additional sequences which are being characterized. The additionalnew sequences may encode other inorganic ion receptors.

This example, like the other examples described herein, is not meant tobe limiting. Various other highly conserved sequence regions can beidentified and utilized in a similar fashion. Such advances are madepossible by the discovery of the parathyroid calcium receptor sequence,as will be recognized by those of ordinary skill in the art. The cloningof such PCR products enables the isolation of complete genomic clonesand of full-length cDNA clones from the tissue sources identified by,for example, Northern analysis using the cloned PCR product. Asadditional members of this family are discovered and their sequencesdetermined, refinement of this approach will be possible. Thus, theinvention herein enables the discovery of more and more members of thisreceptor family via an iterative process.

EXAMPLE 33 Antibodies Against Calcium Receptors

Cloned human and bovine calcium receptors can be used to produceantibodies which recognize various regions of the receptor includingextracellular domains, cytoplasmic domains, extracellular loops andcytoplasmic loops. Recombinant expression of three regions of theN-terminal extracellular domain has been achieved. In particular, GSTfusion products have been produced containing amino acids 9-258 and259-334, respectively, of the bovine parathyroid calcium receptor andamino acids 340-620 from the human parathyroid calcium receptor. Thesefusion products were isolated by preparative SDS-PAGE and injected intorabbits resulting in polyclonal antibodies against the putativeextracellular domain.

In addition, the following synthetic peptides have been produced byMultiple Peptide Systems, Inc:

    ______________________________________                                        SEQ. ID. NO. 9:                                                                              YKDQDLKSRPESVEC,                                               SEQ. ID. NO. 10:                                                                             ADDDYGRPGIEKFREEAEERDIC,                                       SEQ. ID. NO. 11:                                                                             CIDFSELISQYSDEEKIQQ,                                           SEQ. ID. NO. 12:                                                                             YHNGFAKEFWEETFNC,                                              SEQ. ID. NO. 13:                                                                             DGEYSDETDASAC,                                                 SEQ. ID. NO. 14:                                                                             NTPIVKATNRELSYC,                                               SEQ. ID. NO. 15:                                                                             YRNHELEDEIIFITC, and                                           SEQ. ID. NO. 16:                                                                             RKLPENFNEAKYC.                                                 ______________________________________                                    

These amino acid sequence are based upon regions of the bovineparathyroid calcium receptor.

These peptides were conjugated to KLH and injected into rabbits toproduce polyclonal antibodies or injected into mice to producemonoclonal antibodies. Such antibodies are capable of recognizingspecific regions of the bovine parathyroid calcium receptor and mostwould be expected to recognize calcium receptors from other speciesincluding human calcium receptors. Highly acidic peptides (e.g., SEQ.ID. NOs. 9-12 and 15), derived from acid-rich regions of the calciumreceptor may be involved in binding to calcium ion. It is expected,therefore, that such antibodies will be capable, alone or incombination, of neutralizing the calcium receptor by preventing thebinding or action of calcium.

EXAMPLE 34 Recombinant Expression of Parathyroid Calcium Receptors inVertebrate Cells

Recombinant expression of calcium receptors in vertebrate cells can beachieved by inserting cDNA encoding these receptors into appropriateexpression vectors. To assess the best cell line for functionalexpression, the following seven plasmid vectors were constructed usingbovine and human cDNAs encoding parathyroid calcium receptors:

(1) The plasmid pSV-BoPCaR was constructed by subcloning the 5.3 KbpXbaI-SalI fragment from the bovine parathyroid calcium receptor cDNAinto XbaI-XhoI cut pSVL. The expression vector pSVL was purchased fromPharmacia. The vector pSVL contains the SV40 late promoter and VP1processing signals, and is designed to give high levels of expression ina variety of cell lines.

(2) The plasmid CMV-BoPCaR was constructed by subcloning the 5.3 KbpXbaI-SalI fragment from bovine parathyroid calcium receptor intoXbaI-XhoI cut pcDNAI/Amp. The vector pcDNAI/Amp was purchased fromInvitrogen. This vector utilizes the promoter/enhancer sequences fromthe immediate early gene of the human cytomegalovirus to drivehigh-level expression in a variety of cell lines.

(3) The plasmid -471 SportsCaRB, having 471 bp of noncoding sequenceremoved from the 5' end of BoPCaR cDNA, was constructed by subcloning a4.8 Kbp blunt-ended SauI-XbaI fragment of BPoCaR cDNA into SmaI cutpSV-SPORT. The vector pSV-SPORT was purchased from Gibco-BRL. Thisvector utilizes the SV40 early promoter to drive transient expression ina variety of cell lines.

(4) The plasmid CMVHuPCaR4.0 was constructed by subcloning theHindIII-NotI 4.0 Kbp fragment from human calcium receptor cDNA intoHindIII-NotI cut pcDNAI/Amp.

(5) The plasmid CMVHuPCaR5.2 was constructed by subcloning theHindIII-NotI 5.2 Kbp fragment from human calcium receptor cDNA intoHindIII-NotI cut pcDNAI/Amp.

(6) The plasmid pSV-HuPCaR4.0 was constructed by subcloning theSalI-NotI 4.0 Kbp fragment from human calcium receptor cDNA intoSalI-NotI cut pcDNAI/Amp.

(7) The plasmid pSV-HuPCaR5.2 was constructed by subcloning theSalI-NotI 5.2 Kbp fragment from human calcium receptor cDNA intoSalI-NotI cut pcDNAI/Amp.

The above expression vectors were first validated for correctconstruction by in vitro transcription and injection into Xenopusoocytes. All were found to elicit expression of functional calciumreceptors.

Next, these vectors were transfected into a variety of vertebrate cellsincluding: COS7, CHO, DHFR-CHO, HEK293, JEG, Rat2 fibroblasts, MDBK,CV1, UMR, ART20, Y1, OK, LLC-PK1. Several different transfectiontechniques were used including calcium phosphate precipitation,DEAE-dextran, electropotation and lipofection. All the transfected celllines gave rise to substantial levels of calcium receptor transcript.

Functional calcium receptor expression was assessed by loading cellswith fura-2 and measuring changes in intracellular calcium levels afteraddition of calcium receptor agonists. Control constructs were preparedby cloning the substance K receptor and the M1 muscarinic receptor cDNAsinto similar commercial vectors as described above. Control constructswere transfected into the various cell lines described above, and theresponse of the cells containing the control constructs to substance Kor to carbachol, respectively, was measured. Classical responses (i.e.,a rapid and transient increase in internal calcium followed by a lower,sustained increase in internal calcium) were generally observed forcells containing control receptor constructs when treated with theligand appropriate for the receptor being expressed, but not whentreated with an inappropriate ligand. Neither control responded toincreases in extracellular calcium. Similarly, HEK293, CHO and JEG-3cells transfected with the calcium receptor constructs did not respondto substance K or to carbachol. However, a weak, but significant,response was observed in these cells only when extracellular calcium wasincreased from 1 mM to 10 mM.

EXAMPLE 35 Selection of Stable Recombinant Cells Expressing the CalciumReceptor

Clonal cell lines that stably express the two human and the bovinecalcium receptors have been isolated. Calcium receptor cDNAs weresubcloned in two different, commercially available expression vectors;pMSG (obtained from Pharmacia) and Cep4B (obtained from Invitrogen). Thefirst vector contains the selectable marker gene for xanthine-guaninephosphoribosyltransferase (gpt) allowing stably transfected cells toovercome the blockade of the purine biosynthetic pathway imposed byaddition of 2 μg/ml aminopterin and 25 μg/ml mycophenolic acid. Thesecond vector encodes a gene conferring resistance to the antibiotichygromycin (used at 200 μg/ml). HuPCaR 5.2 and HuPCaR 4.0 cDNAs (SEQ.ID. NOs. 2 and 3, respectively) were removed from the parent bluescriptplasmid with Not I and Hind III restriction enzymes and then eitherligated directly into Not I+Hind III digested Cep4B or treated with theklenow fragment of DNA polymerase prior to blunt-end ligation into Sma Idigested pMSG.

The pMSG subclone containing the HuPCaR 5.2 insert was transfected intoCHO cells as discussed above. Selection has resulted in 20 resistantclones which are being characterized. The Cep4B subclone containing theHuPCaR 5.2 insert was transfected into HEK293 cells as described above.Selection with hygromycin resulted .in a pool of stable clones. Clonesexpressing the HuPCaR 4.0 receptor isoform were prepared similarly.

Cells obtained from the pool of hygromycin selected HEK293 cellstransfected with Cep4B containing the HuPCaR 5.2 insert were plated oncollagen coated Aklar squares which had been placed into individualwells of 12-well tissue culture plates. Two to six days later, mediumwas removed and the cells washed with balanced salt solution and 1 ml ofbuffer containing 1 μM fura2-AM, 1 mM CaCl₂ and 0.1% BSA and 1 mM CaCl₂.Measurements of fluorescence in response to calcium receptor agonistswere performed at 37° C. in a spectrofluorimeter using excitation andemission wavelengths of 340 and 510 nm, respectively. For signalcalibration, Fmax was determined after addition of ionomycin (4.0 μM)and the apparent Fmin was determined by addition of 0.3M EGTA, 2.5MTris-HCl; pH 10. Robust increases in intracellular calcium were observedin response to the addition of the following calcium receptor agonists:Ca²⁺ (10 mM), Mg²⁺ (20 mM) and NPS R-467. Control cells expressingfunctional substance K receptors did not respond to these calcimimeticcompounds.

Additional clonal isolates of HEK 293 cells transfected with pHuPCaR4.0sequence were obtained. These were tested for responsiveness tocalcimimetics as described above except that the cells were tested whilein suspension. Similar positive results were obtained (FIG. 28b).

EXAMPLE 36 Activity of NPS R-568 in Xenopus Oocytes Expressing a BovineParathyroid Cell Calcium Receptor

Xenopus oocytes were injected with BoPCaR 1, the 5.3 Kb cDNA encoding abovine parathyroid cell calcium receptor as described in Example 25.After two to three days, Cl⁻ currents were examined in the oocytes usinga two-electrode voltage clamp. In the presence of 0.3 or 1 mMextracellular Ca²⁺, exposure of BoPCaR 1-injected oocytes to NPS R-568caused increases in the Cl⁻ current. The EC₅₀ for NPS R-568 in thisassay was about 3 μM. NPS R-568 failed to evoke responses in uninjectedoocytes or in oocytes injected with water or rat liver mRNA. NPS S-568elicited responses in BoPCaR 1-injected oocytes only at much higherconcentrations (100 μM). The results of these experiments demonstratethat NPS R-568 acts in a stereoselective manner in oocytes expressing abovine parathyroid cell calcium receptor. The data are consistent with adirect action of NPS R-568 on the calcium receptor.

The Cl⁻ current response to NPS R-568 in oocytes expressing BoPCaR 1 wasabolished in the absence of extracellular C²⁺. Increasing theconcentration of extracellular M²⁺ to 4 mM (in the absence ofextracellular Ca²⁺) restored responsiveness to NPS R-568. NPS R-568potentiated the responses to submaximal concentrations of extracellularCa²⁺ and shifted the extracellular Ca²⁺ concentration-response curve tothe left without greatly affecting the maximal response (FIG. 51). Theseeffects obtained in oocytes expressing a parathyroid cell calciumreceptor mirror those obtained in intact bovine parathyroid cells andoffer compelling evidence for a direct effect of NPS R-568 on aparathyroid cell calcium receptor.

The data are also consistent with NPS R-568 increasing the sensitivityof the receptor through an allosteric mechanism by binding to a domainon the calcium receptor distinct from that which binds extracellularCa²⁺. Alternatively, NPS R-568, although binding at the extracellularCa²⁺ domain, may lack intrinsic efficacy unless the domain is partiallyoccupied by extracellular Ca²⁺. The more likely hypothesis is theformer, in which NPS R-568 acts through an allosteric mechanism toincrease the sensitivity of the receptor to activation by extracellularCa²⁺.

The failure of NPS R-568 to elicit responses in the absence ofextracellular Ca²⁺ demonstrates that partial occupancy of the calciumreceptor by extracellular Ca²⁺ is necessary for NPS R-568 to activatethe receptor. It is not presently known if NPS R-568 binds to thecalcium receptor in the absence of extracellular Ca²⁺ or if binding ofextracellular Ca²⁺ to the calcium receptor unmasks a cryptic bindingsite for NPS R-568. These alternative hypotheses can be readily resolvedby direct binding studies using ³ H-NPS R-568 as described above underthe heading of "Allosteric Site on Parathyroid Cell Calcium Receptor."

EXAMPLE 37 Activity of Arylalkyl Polyamines in Xenopus OocytesExpressing a Bovine Parathyroid Cell Calcium Receptor

Xenopus oocytes were injected with BoPCaR 1 as described in Example 25.After two to three days, Cl⁻ currents were examined in the oocytes usingtwo electrode voltage clamp. In the presence of 1 mM extracellular Ca²⁺,exposure of BoPCaR 1-injected oocytes to the arylalkyl polyaminecompounds NPS 017 (shown as AGA 489 in FIG. 1f) or NPS 019 causedoscillatory increases in the Cl⁻ current. Increases in Cl⁻ currentevoked by NPS 019 persisted in the absence of extracellular Ca²⁺.Neither NPS 017 nor NPS 019 elicited changes in Cl⁻ current inuninjected oocytes or in oocytes injected with water or rat liver mRNA.

The results provide compelling evidence for a direct action of arylalkylpolyamine compounds on a parathyroid cell calcium receptor. In authenticbovine parathyroid cells, arylalkyl polyamine compounds mobilizeintracellular Ca²⁺ in the absence of extracellular Ca²⁺ ; they haveidentical effects in oocytes expressing a bovine parathyroid cellcalcium receptor. Also, like the inorganic di- and trivalent cations,the arylalkyl polyamines are positively charged. In the aggregate, theresults suggest that the arylalkyl polyamines act at the same site onthe calcium receptor as does extracellular Ca²⁺.

These data also distinguish the action of arylalkyl polyamines like NPS019 from arylalkylamines like NPS R-568 (see Example 36). These twoclasses of compounds have different mechanisms of action on theparathyroid cell calcium receptor and probably bind at different domainson the receptor. For example, while arylalkyl polyamines can stimulatethe parathyroid calcium receptor in the absence of extracellular Ca²⁺,NPS R-568 requires the presence extracellular Ca²⁺ or an appropriateagonist, such as an arylalkyl polyamine, to stimulate the receptor.Arylalkyl polyamines can completely restore responses to NPS R-568 inthe absence of extracellular Ca²⁺. Moreover, NPS R-568 shifts theconcentration-response curve of NPS 019 to the left.

Arylalkyl polyamines mimic, in all respects tested, the actions ofextracellular divalent cations and are true calcimimetic compounds.Arylalkyl polyamines therefore define a new structural class ofcalcimimetic compounds that act through a different mechanism thancompounds like NPS R-568, probably by binding to a different domain onthe calcium receptor. Arylalkyl polyamines can be used as structuraltemplates for drugs useful in the treatment of various bone andmineral-related disorders.

EXAMPLE 38 Analogs of Arylalkyl Polyamines and Polyamines Useful asAntagonists of Calcium Influx in Parathyroid Cells

Arylalkyl polyamines such as NPS 019 and polyamines such as spermine actas calcimimetics at the parathyroid cell calcium receptor presumably bybinding to the extracellular Ca²⁺ -binding domain on the receptor(Examples 2, 6 and 36). Certain structural analogs of the arylalkylpolyamines or polyamines, in which the secondary amines are replaced bymethylenes, act as blockers of Ca²⁺ influx in parathyroid cells. NPS 384and NPS 472 (1,12-diaminododecane, see FIG. 1a) are arylalkyl polyamineand polyamine analogs, respectively, lacking secondary amines. Whentested at high micromolar concentrations (100 to 1000 μM), either ofthese compounds causes a prompt fall in Ca²⁺ !_(i) in bovine parathyroidcells bathed in buffer containing 2 mM CaCl₂. Pretreatment ofparathyroid cells with either of these compounds depresses steady-state,but not transient increases in Ca²⁺ !_(i) elicited by increasing theconcentration of extracellular Ca²⁺. In both these respects, the effectsof NPS 384 and NPS 472 are similar to low concentrations of La³⁺ or Gd³⁺which block Ca²⁺ influx.

Structural analogs of NPS 384 and NPS 472 with greater potency forblocking Ca²⁺ influx in parathyroid cells can be synthesized bymodification of the aromatic moiety or alkyl chain. Compounds that blockthe influx of extracellular Ca²⁺ in parathyroid cells may findtherapeutic utility in the treatment of various bone and mineral-relateddisorders. For example, it is known that the level of extracellular Ca²⁺can regulate the mRNA levels for PTH. Thus, blocking the influx ofextracellular Ca²⁺ may increase mRNA levels for PTH. Such an increase inmRNA transcripts would be expected to increase PTH synthesis, resultingin a larger reserve of PTH for secretion. Calcilytic compounds mighttherefore cause an augmented release of PTH when administered after adrug that blocks influx of extracellular Ca²⁺ in parathyroid cells.

EXAMPLE 39 Activity of NPS R-568 and Arylalkyl Polyamines in XenopusOocytes Expressing a Human Parathyroid Cell Calcium Receptor

Xenopus oocytes were injected with pHuPCaR 5.2, the 5.2 Kb cDNA encodinga parathyroid cell calcium receptor derived from a human parathyroidcell adenoma. (See Example 27.) After two to three days, Cl⁻ currentswere measured in the oocytes using a two-electrode voltage clamp. In thepresence of 0.3 mM extracellular Ca²⁺, both NPS R-568 or NPS 019 (3 to30 μM) evoked increases in the Cl⁻ current indicating activation of theexpressed calcium receptor. In the absence of extracellular Ca²⁺, theresponse to NPS 019 persisted whereas that to NPS R-568 was abolished.In Xenopus oocytes expressing a human parathyroid cell calcium receptor,NPS R-568 shifted the concentration-response curve to the left withoutgreatly altering the maximal response. Thus, a human parathyroid cellcalcium receptor responds to NPS R-568 and to NPS 019 similarly tobovine parathyroid cells.

EXAMPLE 40 Activity of NPS R-467 and NPS R-568 on C-Cells

C-cells appear to express a calcium receptor that is structurallysimilar to that present on parathyroid cells (see Example 31). Theeffects of NPS R-467 and NPS R-568 on Ca²⁺ !_(i) in a rat medullarythyroid carcinoma E-cell line (44-2 cells) were examined. In thepresence of extracellular Ca²⁺ (1 mM), either compound evoked aconcentration-dependent increase in Ca²⁺ !_(i). Both compounds were lesspotent on C-cells than bovine parathyroid cells. The EC_(50's) for NPSR-467 and NPS R-568 were 1.9 and 2.2 μM, respectively. Thus, compoundsin this structural series appear to activate the C-cell calciumreceptor.

Arylalkyl polyamines likewise elicit increases in Ca²⁺ !_(i) in C-cellsas they do in parathyroid cells (see Examples 6 and 13). Some arylalkylpolyamines are more potent on C-cells than on parathyroid cells. Thus,compounds structurally related to NPS R-568, but with greater potency onC-cells compared to parathyroid cells, may reside in the compoundlibrary illustrated in FIG. 36. Compounds more potent on C-cells thanparathyroid cells could be used to selectively increase calcitoninsecretion while having little or no effect on PTH secretion.

EXAMPLE 41 NPS R-568 Increases Calcitonin Secretion In Vivo

Normal adult Sprague-Dawley rats were administered various doses of NPSR-568 p.o. At various times following the administration of NPS R-568,blood samples were withdrawn and measured for PTH, ionized Ca²⁺, andcalcitonin. NPS R-568 caused a rapid, dose-dependent decrease in theplasma levels of PTH and Ca²⁺ and an increase in calcitonin. The ED₅₀values for the depression of PTH and Ca²⁺ and stimulation of calcitoninwere 1, 8 and 40 mg/kg p.o. Thus, the oral administration of NPS R-568suppresses plasma levels of PTH at doses lower than those which increaseplasma levels of calcitonin.

In subsequent studies, rats received a thyroidectomy (parathyroid glandsintact). This surgical procedure effectively removed the C-cellssecreting calcitonin and therefore enabled the relative contributions ofPTH and calcitonin to the hypocalcemic effect of this compound to bedetermined. In thyroidectomized animals, the administration of NPS R-568(3 to 100 mg/kg p.o.) caused a hypocalcemic response equal in magnitudeto that produced in sham-operated animals. The only difference was thatthe rate of onset of the hypocalcemic response was somewhat delayed inthyroidectomized animals. Thus, the major action of NPS R-568 causingthe hypocalcemic response is an inhibition of PTH secretion. Stimulatoryeffects of this compound on calcitonin secretion increases the rate ofonset, but not the extent, of hypocalcemia.

EXAMPLE 42 Effectiveness of NPS R-568 in Humans

NPS R-568 was studied in a placebo-controlled, single-dose,dose-escalation format in a healthy, post-menopausal woman. A range ofsingle oral doses was used to assess safety, tolerance, and changes inprimary hyperparathyroidism markers (e.g., plasma concentrations ofparathyroid hormone and ionized serum calcium) and of serum calcitonin.The data are shown in Tables 8-10.

                  TABLE 8                                                         ______________________________________                                        Effect of NPS R-568 on Serum Parathyroid Hormone in a Human                   TIME (hours)                                                                  DOSE     0     0.5     1   2     4   8     12  24                             ______________________________________                                        Serum PTH (pg/ml)                                                             Placebo  34    32      32  34    32  36    44  32                             20 mg    31    23      18  24    34  34    48  32                             240 mg   29    18      6   6     10  27    35  34                             400 mg   33    13      9   8     11  20    31  31                             ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        Effect of NPS R-568 on Serum Ionized Calcium in a Human                       TIME (hours)                                                                  DOSE  0       0.5    1    2     4    8    12   24                             ______________________________________                                        Serum Ionized Calcium (mg/dl)                                                 Placebo                                                                             1.24    1.23   1.24 1.24  1.25 1.23 1.23 1.23                           20 mg 1.26    1.26   1.26 1.26  1.26 1.26 1.23 1.29                           240 mg                                                                              1.26    1.26   1.25 1.23  1.19 1.16 1.18 1.23                           400 mg                                                                              1.24    1.26   1.25 1.22  1.19 1.13 1.15 1.22                           ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        Effect of NPS R-568 on Serum Calcitonin in a Human                            TIME (hours)                                                                  DOSE     0     0.5     1   2     4   8     12  24                             ______________________________________                                        Serum Calcitonin (pg/ml)                                                      Placebo  3.5   4.0     3.8 4.2   3.9 3.6   3.4 3.4                            20 mg    3.2   3.8     3.2 4.5   4.2 3.9   3.2 3.6                            240 mg   5.8   4.8     6.5 7.5   6.1 4.7   5.3 8.3                            400 mg   3.4   4.0     6.0 7.1   5.2 3.8   3.7 3.0                            ______________________________________                                    

The data illustrated in Tables 8-10 indicate that NPS R-568 causes atransient dose-dependent decrease in plasma PTH concentration (Table 8),and, at higher doses, a decrease in serum ionized calcium concentration(Table 9) in the human subject. There was no apparent change in serumcalcitonin at the doses studied (Table 10). Higher doses are expected toaffect calcitonin levels as observed in rats (see Example 41).

EXAMPLES 43-54

Examples 43 to 54 describing the syntheses of compounds 4L, 8J, 8U, 9R,11X, 12U, 12V, 12Z, 14U, 17M and 17P, are provided below. Compounds 4L,8J, 8U, 11X and 17M were prepared from the condensation of a primaryamine with an aldehyde or ketone in the presence of titanium(IV)isopropoxide. The resulting intermediate imines were then reduced insitu by the action of sodium cyanoborohydride, sodium borohydride, orsodium triacetoxyborohydride. The intermediate enamine for the synthesisof compound 8U was catalytically reduced using palladium hydroxide.

Compounds 9R, 14U, and 17P were synthesized by reductive amination of acommercially available aldehyde or ketone with a primary amine in thepresence of sodium cyanoborohydride or sodium triacetoxyborohydride. Itwas found for the syntheses of these three compounds (9R, 14U, and 17P)that sodium triacetoxyborohydride afforded the desired diastereomerswith greater diastereoselectivity than using sodium cyanoborohydride.The enriched mixtures were further purified to a single diastereomer bynormal-phase HPLC or by recystallization.

Compounds 12U, 12V and 12Z were prepared by a diisobutylaluminum hydride(DIBAL-H)-mediated condensation of an amine with a nitrile. Theresulting intermediate imine is reduced in situ by the action of sodiumcyanoborohydride or sodium borohydride. The intermediate alkenes(compounds 12U and 12V) were reduced by catalytic hydrogenation in EtOHusing palladium on carbon. Compounds which were converted to theircorresponding hydrochlorides were done so by treatment of the free basewith ethereal HCl to afford white solids.

The starting materials for these syntheses were: (1) purchased fromAldrich Chemical Co., Milwaukee, Wis. (2) purchased from Celgene Corp.,Warren, N.J., or (3) prepared synthetically using standard techniquesknown in the art. All other reagent chemicals were purchased fromAldrich Chemical Co.

EXAMPLE 43 Synthesis of Compound 4L

N-3-Phenyl-1-propyl-1-(1-naphthyl)ethylamine

A mixture of 3-phenyl-1-propylamine (135 mg, 1 mmol), 1'-acetonaphthone(170 mg, 1 mmol), and titanium (IV) isopropoxide (355 mg, 1.3 mmol) wasstirred at room temperature for 1 hour. The reaction was treated with 1Methanolic sodium cyanoborohydride (1 mL) and stirred at room temperaturefor 16 hours. The reaction was diluted with ether and treated with water(0.1 mL). The reaction was centrifuged and the ether layer removed andconcentrated to a milky oil. A small portion of this material (10 mg)was purified by HPLC (Phenomenex, 1.0×25 cm, 5-μM silica) using agradient of dichloromethane to 10% methanol in dichloromethanecontaining 0.1% isopropylamine. This afforded the product (free base) asa single component by GC/EI-MS (R_(t) =10.48 min) m/z (rel. int.) 289(M⁺, 11), 274 (63), 184 (5), 162 (5), 155 (100), 141 (18), 115 (8), 91(45), and 77 (5).

EXAMPLE 44 Synthesis of Compound 8J

N-(3-Phenylpropyl)-1-(3-thiomethylphenyl)ethylamine hydrochloride

3'-Aminoacetophenone (2.7 g, 20 mmol) was dissolved in 4 mL ofconcentrated HCl, 4 g of ice and 8 mL of water. The solution was cooledto 0° C., and sodium nitrite (1.45 g, 21 mmol) dissolved in 3-5 mL ofwater was added over 5 minutes while maintaining the temperature below6° C. Sodium thiomethoxide (1.75 g, 25 mmol) was dissolved in 5 mL ofwater and cooled to 0° C. To this solution was added the diazonium saltover 10 minutes while maintaining the temperature below 10° C. Thereaction was stirred for an additional hour while allowing thetemperature to rise to ambient. The reaction mixture was partitionedbetween ether and water. The ether layer was separated and washed withsodium bicarbonate and sodium chloride, and dried over sodium sulfate.The ether was evaporated to give a 74% yield of3'-thiomethylacetophenone. The crude material was purified bydistillation at reduced pressure.

3-Phenylpropylamine (0.13 g, 1 mmol), 3'-thiomethylacetophenone (0.17 g,1 mmol), and titanium (IV) isopropoxide (0.36 g, 1.25 mmol) were mixedtogether and allowed to stand for 4 hours. Ethanol (1 mL) and sodiumcyanoborohydride (0.063 g, 1 mmol) were added and the reaction wasstirred overnight. The reaction was worked up by the addition of 4 mL ofether and 200 μL of water. The mixture was vortexed and then spun in acentrifuge to separate the solids. The ether layer was separated fromthe precipitate, and the solvent removed, in vacuo. The oil wasredissolved in dichloromethane and the compound purified by preparativeTLC on silica gel eluted with 3% methanol-dichloromethane to yield thetitle compound as a pure oil: GC/EI-MS (R_(t) =7.64 min) m/z (rel.int.)285 (M⁺, 18), 270(90), 180(17), 151(100), 136(32), 104(17), 91(54),and 77(13).

EXAMPLE 45 Synthesis of Compound 8U

(R)-(+)-N-3-(2-Methoxyphenyl)-1-propyl-3-methoxy-α-methylbenzylaminehydrochloride

A mixture of (R)-(+)-3-methoxy-α-methylbenzylamine (3.02 g, 20 mmol),2-methoxycinnamaldehyde (3.24 g, 20 mmol), and titanium (IV)isopropoxide (8.53 g, 30 mmol, 1.5 eq.) was stirred for 2 hours at roomtemperature and treated with 1M (20 mL) ethanolic sodiumcyanoborohydride. The reaction was stirred overnight (16 hours), dilutedwith diethyl ether, and treated with water (1.44 mL, 80 mmol, 4 eq.).After mixing for 1 hour, the reaction mixture was centrifuged and theether layer removed and concentrated to an oil. This material wasdissolved in glacial acetic acid, hydrogenated at 60 p.s.i. hydrogen inthe presence of palladium hydroxide for 2 hours at room temperature. Thecatalyst was removed by filtration and the resulting solutionconcentrated to a thick oil. This material was dissolved indichloromethane and neutralized with 1N NaOH. ,The dichloromethanesolution was separated from the aqueous phase, dried over anhydrouspotassium carbonate and concentrated to an oil. This material wasdissolved in ether and treated with 1M HCl in diethylether. Theresulting precipitate (white solid) was collected, washed with diethylether, and air dried. GC/EI-MS (R_(t) =9.69 min) of this material (freebase) showed a single component: m/z (rel. int.) 299 (M+, 21), 284(100), 164 (17), 150 (8), 135 (81), 121 (40), 102 (17), 91 (43), and 77(18).

EXAMPLE 46 Synthesis of Compound 9R

(R,R)-N-(1-(2-Naphthyl)ethyl)-1-(1-naphthyl)ethylamine hydrochloride

A mixture of (R)-(+)-1-(1-naphthyl) ethylamine (10.0 g, 58 mmol),2'-acetonaphthone (9.4 g, 56 mmol), titanium (IV) isopropoxide (20.7 g,73.0 mmol), and EtOH (abs.) (100 mL) was heated to 60° C. for 3 hours.Sodium cyanoborohydride (NaCNBH₃) (3.67 g, 58.4 mmol) was then added.The reaction mixture was stirred at room temperature for 18 hours. Ether(1 L) and H₂ O (10 mL) were added to the reaction mixture and theresulting precipitate was removed by centrifugation. The supernatant wasevaporated under vacuum and the crude product was recrystallized fourtimes from hot hexane, to provide 1.5 g of pure (98+%) diastereomer. Thefree base was dissolved in hexane, filtered, and then ethereal HCl wasadded to precipitate the product as a white solid (1.1 g, 6% yield),m.p.: softens 200°-240° C. (dec.).

EXAMPLE 47 Synthesis of Compound 11X

(R)-N-(4-Isopropylbenzyl)-1-(1-naphthyl)ethylamine hydrochloride

A mixture of (R)-(+)-1-(1-naphthyl) ethylamine (1.06 g, 6.2 mmol),4-isopropylbenzaldehyde (0.92 g, 6.2 mmol), and titanium (IV)isopropoxide (2.2 g, 7.7 mmol) was heated to 100° C. for 5 min thenallowed to stir at room temperature for 4 hours. Sodium cyanoborohydride(NaCNBH₃) (0.39 g, 6.2 mmol) was then added followed by EtOH (1 mL). Thereaction mixture was stirred at room temperature for 18 hours. Ether(100 mL) and H₂ O (1 mL) were added to the reaction mixture and theresulting precipitate was then removed by centrifugation. Thesupernatant was evaporated under vacuum and the crude product waschromatographed on silica gel (50 mm×30 cm column) (elution with 1%MeOH/CHCl₃). The chromatographed material was then dissolved in hexaneand ethereal HCl was added to precipitate the product as a white solid(0.67 g, 35% yield); m.p. 257°-259° C.

EXAMPLE 48 Synthesis of Compound 12U

(R)-N-3-(2-Methylphenyl)-1-propyl-3-methoxy-α-methylbenzylaminehydrochloride

A solution of 2-methylcinnamonitrile (1.43 g, 10 mmol) indichloromethane (10 mL) was cooled to 0° C. and treated dropwise (15minutes) with 1M diisobutylaluminum hydride (10 mL, dichloromethane).The reaction was stirred for at 0° C. for 15 minutes and treateddropwise (15 minutes) with a 1M solution of(R)-(+)-3-methoxy-α-methylbenzylamine (1.51 g, 10 mmol) indichloromethane (10 mL). The reaction was stirred for 1 hour at 0° C.and poured into a solution of ethanol (100 mL) containing sodiumcyanoborohydride (1 g, 16 mmol). The reaction mixture was stirred 48hours at room temperature. The reaction was diluted with diethyl etherand neutralized with 1N NaOH. The diethyl ether layer was removed, driedover anhydrous potassium carbonate and concentrated to an oil. Thismaterial was chromatographed through silica using a gradient ofdichloromethane to 5% methanol in dichloromethane to afford theunsaturated intermediate, a single component by GC/EI-MS (R_(t) =10.06min) m/z (rel. int.) 281 (M⁺, 17), 266 (59), 176 (19), 146 (65), 135(73), 131 (100), 91 (21), and 77 (13).

The unsaturated intermediate in ethanol was hydrogenated (1 atm H₂) inthe presence of palladium on carbon for 16 hours at room temperature.The product from this reaction was converted to the hydrochloride saltby treatment with 1M HCl in diethyl ether. GC/EI-MS (R_(t) =9.31 min) ofthis material (free base) showed a single component: m/z (rel. int.) 283(M+, 21), 268 (100), 164 (12), 148 (8), 135 (85), 121 (12), 105 (49), 91(23), and 77 (21).

EXAMPLE 49 Synthesis of Compound 12V

(R)-N-3-(3-Methylphenyl)-1-propyl-3-methoxy-α-methylbenzylaminehydrochloride

The compound was prepared following the procedure described in Example48, but using 2-methylcinnamonitrile. The unsaturated intermediate was asingle component by GC/EI-MS (R_(t) =10.21 min) m/z (tel. int.).281 (M⁺,57), 266 (86), 146 (98), 135 (88), 131 (100), 115 (43), 102 (26), 91(43), and 77 (18). Reduction of this material and hydrochlorideformation using the procedure described in Example 48 afforded theproduct. GC/EI-MS (R_(t) =9.18 min) of this material (free base) showeda single component; m/z (rel. int.) 283 (M⁺, 19), 268 (100), 164 (11),148 (8), 135 (76), 121 (16), 105 (45), 91 (23), and 77 (21).

EXAMPLE 50 Synthesis of Compound 12Z

(R)-N-3-(2-Chlorophenyl)-1-propyl-1-(1-naphthyl)ethylamine hydrochloride

The compound was prepared following the procedures described in Example48, but using 2-chlorohydrocinnamonitrile and(R)-(+)-1-(1-naphthyl)ethylamine on a 10-mmol scale. Chromatographythrough silica gel using a gradient of dichloromethane to 5% methanol indichloromethane afforded the product as a single component by silic gelTLC analysis (5% methanol in dichloromethane). The hydrochloride wasprepared by treatment with 1M HCl in diethyl ether.

EXAMPLE 51 Synthesis of Compound 14U

(R,R)-N-(1-(4-Methoxyphenyl)ethyl)-1-(1-naphthyl)ethylaminehydrochloride

A mixture of (R)-(+)-1-(1-naphthyl)ethylamine (1.1 g, 6.2 mmol),4'-methoxyacetophenone (0.93 g, 6.2 mmol), titanium (IV) isopropoxide(2.2 g, 7.7 mmol), and EtOH (abs.) (1 mL) was heated to 60° C. for 3hours. Sodium cyanoborohydride (NaCNBH₃) (0.39 g, 6.2 mmol) was thenadded, and the reaction mixture was stirred at room temperature for 18hours. Ether (200 mL) and H₂ O (2 mL) were added to the reaction mixtureand the resulting precipitate was then removed by centrifugation. Thesupernatant was evaporated under vacuum and the crude product waschromatographed on silica gel (25 mm×25 cm column) (elution with 1%MeOH-CHCl₃). A portion of this material was HPLC chromatographedSelectosil, 5-μM silica gel; 25 cm×10.0 mm (Phenomenex, Torrance,Calif.), 4 mL per minute; UV det. 275 nm; 12% ethyl acetate-88% hexane(elution time, 12.0 min)!. The HPLC purified diastereomer was thendissolved in hexane and ethereal HCl was added to precipitate theproduct as a white solid (20 mg), m.p. 209°-210° C. (dec.).

EXAMPLE 52 Synthesis of Compound 17M

(R)-N-(3-Chloro-4-methoxybenzyl)-1-(1-naphthyl)ethylamine hydrochloride

A mixture of (R)-(+)-1-(1-naphthyl)ethylamine (6.6 g, 39 mmol),3'-chloro-4'-methoxybenzaldehyde (6.6 g, 39 mmol), titanium (IV)isopropoxide (13.8 g, 48.8 mmol), and EtOH (abs.) (30 mL) was heated to80° C. for 30 minutes and then stirred at room temperature for 3 hours.Sodium cyanoborohydride (NaCNBH₃) (2.45 g, 39 mmol) was then added andthe reaction mixture was stirred at room temperature for an additional18 hours. Diethyl ether (100 mL) and H₂ O (2 mL) were then added to thereaction mixture and the resulting precipitate was removed bycentrifugation. The supernatant was evaporated under vacuum and thecrude product was chromatographed on silica gel (50 mm×30 cm column)(elution with CH₂ Cl₂). The chromatographed material was then dissolvedin hexane (500 mL), decolorized with Norit®, filtered (0.2 μM), and thenethereal HCl was added to precipitate the product as a while solid (10.2g, 56% yield), m.p. 241°-242° C. (dec.).

EXAMPLE 53 Synthesis of Compound 17P

4-Methoxy-3-methylacetophenone 17P Precursor!

A mixture of 4'-hydroxy-3'-methylacetophenone (5.0 g, 33.3 mmol),iodomethane (5.7 g, 40.0. mmol), K₂ CO₃ (granular, anhydrous) (23.0 g,167 mmol), and acetone (250 mL) was refluxed for 3 hours. The reactionmixture was then cooled to room temperature, filtered to remove theinorganic salts, and evaporated under vacuum. The crude product wasdissolved in ether (100 mL) and washed with H₂ O (2×20 mL). The organiclayer was dried (Na₂ SO₄) and evaporated to yield 4.5 g, 82.4% yield.The ketone was used in the following reaction without furtherpurification.

(R,R)-N-(1-(4-Methoxy-3-methylphenyl)ethyl)-1-(1-naphthyl)ethylaminehydrochloride Compound 17P!

A mixture of (R)-(+)-1-(1-naphthyl) ethylamine (4.24 g, 24.8 mmol),4'-methoxy-3'-methylacetophenone (4.06 g, 24.8 mmol), titanium (IV)isopropoxide (8.8 g, 30.9 mmol), and EtOH (abs.) (1 mL) was heated to100° C. for 2 hours. Isopropanol (45 mL) was added and the reaction wascooled to 10° C. in an ice bath. Sodium triacetoxyborohydride NaHB(O₂CCH₃)₃, 10.5 g, 49.5 mmol was then added in portions over 15 minutes.The reaction mixture was then heated to 70° C. for 18 hours. The mixturewas cooled to room temperature and pouted into ether (400 mL). Thesuspension was centrifuged, the supernatant was collected and the pelletwas washed with ether (400 mL). The combined organic washings wereevaporated under vacuum. The residue was dissolved in ether (400 mL) andwashed with 1N NaOH (4×50 mL) and H₂ O (2×50 mL). The organic layer wasdried (Na₂ SO₄), filtered and evaporated under vacuum. EtOH (abs.) wasadded to the wet residue, which was then dried thoroughly on a rotaryevaporator to provide an oil. The mixture was then chromatographed onsilica gel (50 mm×30 cm) elution with (1% MeOH-1% isopropylamine-CHCl₃)to give 4.8 g of an oil!.

The desired diastereomer was further purified by HPLC chromatographySUPELCOSIL™ PLC-Si, 18-μM silica gel; 25 cm×21.2 mm (Supelco, Inc.,Bellefonte, Pa.), 7 mL per minute; UV det. 275 nm: 20% EtOAc-80% hexane(elution time 9.5-11.0 min)!. Injections (800-μL aliquots) of themixture (100 mg/mL solution in eluent) provided 65 mg of the desiredisomer. Multiple HPLC injections provided 1.0 g of purified material.The HPLC-chromatographed material was dissolved in hexane (50 mL) andthe hydrochloride salt was precipitated with ethereal HCl. The salt wascollected on fritted glass and washed with hexane to provide 1.0 g of awhite solid, mp 204°-205° C.

EXAMPLE 55 Synthesis of Compound 17X

3-Chloro-4-methoxybenzaldehyde

A mixture of 3-chloro-4-hydroxybenzaldehyde (25 g, 160 mmol),iodomethane (27.25 g, 192 mmol), K₂ CO₃ (granular, anhydrous) (110.6 g,800 mmol), and acetone (300 mL) was refluxed for 3 hours. The reactionmixture was then cooled to room temperature. Diethyl ether (500 mL) wasadded and the mixture was filtered through paper to remove the inorganicsolids. the filtrate was evaporated under reduced pressure, dissolved indiethyl ether (800 mL), and washed with 0.1N NaOH (3×100 mL). Theorganic layer was dried (Na₂ SO₄) and evaporated under vacuum to yield24 g, 92% yield of crude product. This material was further purified bychromatography on silica gel (50 mm×30 cm) (elution with hexane-EtOAc,5:1) to give 15.02 g, 56% yield of a white solid: TLC (hexane-EtOAc,5:1) R_(f) =0.24; GC R_(t) =4.75 min; MS (EI) m/z 170(M⁺), 172(M+2).

1-Methyl-(3'-chloro-4'-methoxybenzyl) alcohol

A mixture of 3-chloro-4-methoxybenzaldehyde (13 g, 76.5 mmol),methylmagnesium chloride (52 g, 153 mmol), and THF (300 mL) was refluxedfor 3 hours. The reaction mixture was cooled to room temperature. NH₄ Cl(satd. soln., 6 mL) was added dropwise followed by diethyl ether (500mL) and the mixture was filtered through paper to remove the inorganicsolids. The filtrate was evaporated under reduced pressure and theresulting solid was dissolved in diethyl ether (300 mL) and washed withwater (4×25 mL). The organic layer was dried (Na₂ SO₄) and evaporatedunder vacuum to yield 11.3 g, 80% yield of crude product. This materialwas further purified by chromatography on silica gel (50 mm×30 cm)(elution with CH₂ Cl₂) to yield 11.3 g, 63% yield of an oil; TLC (CH₂Cl₂) R_(f) =0.25; GC R_(t) =5.30 min; MS (EI) m/z 186(M⁺), 188(M+2).

3'-Chloro-4'-methoxyacetophenone

A mixture of 1-methyl-(3'-Chloro-4'-methoxybenzyl) alcohol (7.6 g, 41mmol), pyridinium chlorochromate (PCC) (13.16 g, 61.5 mmol), and CH₂ Cl₂(300 mL) was allowed to stir at room temperature for 2 hours. Diethylether (1000 mL) was added and the resulting mixture was placed on achromatography column of silica gel (50 mm×30 cm) (elution with diethylether) to yield 7.3 g, 97% yield of crude solid product. GC analysis ofthis material showed it to be 99% pure and it was used in the followingreaction without further purification. TLC (diethyl ether) R_(f) =1.0;GC R_(t) =5.3 min; MS (EI) m/z 184 (M⁺), 184 (M+2) .

(R,R)-N-(1-Ethyl-4'-methoxy-3'-chlorophenyl )-1-(1-naphthylethyl)amine

A mixture of 3'-chloro-4'-methoxyacetophenone (5.3 g, 29 mmol),(R)-(+)-1-(1-naphthyl) ethylamine (4.98 g, 29 mmol), titanium (IV)isopropoxide (10.2 g, 36 mmol), and isopropanol (20 mL) was heated to100° C. for 3 hours. Sodium triacetoxy-borohydride (NaB(O₂ CCH₃)₃ ;12.29 g, 58 mmol) was added in portions over 10 minutes. The reactionmixture was heated to reflux for 30 minutes and was then allowed to stirat room temperature for 18 hours. The mixture was then poured intodiethyl ether (500 mL); H₂ O (2 mL) was added and the suspension wascentrifuged to remove the fine precipitate of titanium salts. Thesupernatant was collected and the pellet was washed with ether (500 mL).The combined organic layers were dried (Na₂ SO₄) and evaporated undervacuum to yield 6.81 g, 70% of crude product.

This material was further purified by chromatography on silica gel (50mm×30 cm) (elution with 3% MeOH-97% CH₂ Cl₂) to give 2.01 g of an oil.The diastereomer was further purified by recrystallization. The freebase (1.98 g) was converted to its HCl salt with ethereal HCl. This saltwas dissolved in hot isopropanol (65 mL) and the solution was filteredthrough paper. The filtrate was evaporated under vacuum and theresulting solid dissolved in isopropanol (30 mL). After standing at roomtemperature for 18 hours, the crystalline solid was collected, washedwith cold isopropanol (20 mL), and dried to yield 0.87 g, 40% (from freebase) of the diastereomerically pure hydrochloride salt: mp 236°-237° C.(dec); TLC (MeOH-CH₂ Cl₂ 99:1!) R_(f) =0.25; GC R_(t) =11.06 min; FTIR(KBr pellet, cm⁻¹) 3433, 2950, 2931, 2853, 2803, 2659, 2608, 2497, 1604,1595, 1504, 1461, 1444, 1268, 1260, 1067, 1021, 802, 781, 733; MS (EI)m/z 339(M⁺), 341(M+2).

Other embodiments are within the following claims.

We claim:
 1. A purified nucleic acid comprising at least 20 contiguousnucleotides of a nucleic acid sequence provided in SEQ ID NO:
 1. 2. Thepurified nucleic acid of claim 1 comprising 27 contiguous nucleotides ofsaid nucleic acid sequence.
 3. The purified nucleic acid of claim 1comprising at least 45 contiguous nucleotides of said nucleic acidsequence.
 4. A purified nucleic acid comprising a nucleic acid sequenceencoding at least 12 contiguous amino acids of an amino acid sequenceprovided in SEQ ID NO:
 5. 5. The purified nucleic acid of claim 4,wherein said nucleic acid encodes at least 18 contiguous amino acids ofsaid amino acid sequence.
 6. The purified nucleic acid of claim 5wherein said nucleic acid encodes at least 54 contiguous amino acids ofsaid amino acid sequence.
 7. The purified nucleic acid of claim 4wherein said nucleic acid encodes an extracellular binding domain, butis substantially free of transmembrane and intracellular domainportions.
 8. The purified nucleic acid of claim 4 wherein the nucleicacid encodes an intracellular domain but is free of transmembrane andextracellular domains.
 9. The purified nucleic acid of claim 4 whereinthe nucleic acid encodes a transmembrane domain but is free ofintracelluar and extracellular domains.
 10. The purified nucleic acid ofclaim 4 wherein the nucleic acid encodes an extracellular bindingdomain, and said nucleic acid encoding an extracellular binding domainis transcriptionally coupled to a second nucleic acid encodingtransmembrane and intracellular coding domains of a non-inorganic ionreceptor.
 11. A purified nucleic acid comprising a nucleotide sequencewhich comprises at least 16 nucleotides hybridizing under stringentconditions to at least 20 contiguous nucleotides provided in SEQ IDNO:1.
 12. A purified nucleic acid comprising a nucleotide sequence whichcomprises at least 18 nucleotides hybridizing under stringent conditionsto at least 20 continuous nucleotides provided in SEQ ID NO:1.
 13. Apurified nucleic acid comprising a nucleotide sequence which comprisesat least 19 nucleotides hybridizing under stringent conditions to atleast 20 contiguous nucleotides provided in SEQ ID NO:1.
 14. A purifiednucleic acid comprising a nucleotide sequence which comprises at least20 nucleotides hybridizing under stringent conditions to at least 20contiguous nucleotides provided in SEQ ID NO:1.
 15. A purified nucleicacid comprising a nucleic acid sequence selected from the consisting of:SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO:
 8. 16. Thenucleic acid of claim 15, wherein said nucleic acid sequence is SEQ IDNO:
 5. 17. The nucleic acid of claim 15, wherein said nucleic acidsequence is SEQ ID NO:
 6. 18. The nucleic acid of claim 15, wherein saidnucleic acid sequence is SEQ ID NO:
 7. 19. The nucleic acid of claim 15,wherein said nucleic acid sequence is SEQ ID NO:
 8. 20. A purifiednucleic acid comprising a nucleic acid sequence encoding an amine acidsequence selected from the group consisting of SEQ ID NO:
 5. SEQ IDNO:6, SEQ ID NO:7 and SEQ ID NO:
 8. 21. The nucleic acid of claim 20,wherein said amine acid sequence is SEQ ID NO:
 5. 22. The nucleic acidof claim 20, wherein said amine acid sequence is SEQ ID NO:
 6. 23. Thenucleic acid of claim 20, wherein said amine acid sequence is SEQ ID NO:7.
 24. The nucleic acid of claim 20, wherein said amino acid sequence isSEQ ID NO: 8.